Treatise on the WASD Disadvantage

Many games are shipped with a "standard" key configuration, which is supported by gaming keyboards such as the Z-board. This key configuration has many shortcomings. It's a key configuration that doesn't support lefties: those of us who use our left hand to control the mouse. It doesn't help streamline tactics; many keys become unusable. While the key configuration is logical in movement, it defies real-world logic. This is what I call the "WASD key configuration" and it puts a gamer at a disadvantage.
Before I point out the disadvantages, there are a few things that one needs to know. First, I'll define what "mutually exclusive" means. In life, many events are mutually exclusive. If you are walking forward, then you cannot be walking backwards; these events are mutually exclusive. If you are stepping to the right, then you are not moving left; these are also mutually exclusive. Other examples are jumping and crouching, although some may claim you can (quite impossibly) jump while you crouch. "Mutually exclusive" events mean that you can not do them simultaneously.
Second, the human brain is an amazing thing. It processes hundreds of things going on in our body at the same time. While it does this, we learn new things; we program our brains to learn things like typing, shooting a basketball, etc. At a science museum, there were special goggles that "shifted" the basketball goal to the right, so when you shot straight, the basketball missed to the left; however, if you left the glasses on long enough, you could coordinate your hands to shoot the proper distance and direction.
Now, I don't waste my time with the WASD configuration. I'm left-handed, and shift everything to the right-hand side of the keyboard so I can aim with the mouse and use the home keys of the right hand for navigation and activation. I often have to use the semi-colon and single-quote keys, so when a game comes out that disallows me to use them or to reconfigure the controls entirely, I usually dislike the closed-mindedness of the programmers. However, I will keep everything standard for now.
Let's take a look at the WASD configuration keys: 'W'=move forward, 'A'=strafe left, 'S'=move backward, 'D'=strafe right, and (typically) SPACE=jump. Lining your fingers on the keys places one finger on the 'A' key, one finger on the 'S' key, and one finger on the 'D' key. The same finger that is on the 'S' key is used for the 'W' key: the same finger that moves you forward will move you backward.
The finger used for the 'S' key and 'W' key is optimal; that is, it's one finger used for two mutually exclusive events. If you're using that finger to move forward, the keys that the finger uses are, essentially, "dead"; unless you are able to span your finger across multiple keys while maintaining the other digits, you cannot press those keys. This is optimal because you wouldn't want to press the same key to move backward if you're going forward.
The 'A' and 'D' keys provide the biggest problem: they are not optimal. Two mutually exclusive events (strafing left and strafing right) are on two separate fingers. If you're moving left, you wouldn't want to strafe right: when you press the 'A' key to move left, the 'D' key is "dead." It would be better to have this key assigned to an event that is not mutually exclusive to strafing left, like "launch grenade," or "change weapon". But then the question arises: "If I re-bind that key, how do I strafe right?" Answer: optimize by binding the key to your strafing finger. Strafing left is mutually exclusive to strafing right, and thus both should be on one finger. If I'm using the finger to strafe right, I can't strafe left, but I can't strafe left anyways because I'm strafing right.
Let's back up a bit to look at the navigational key bindings. Now, when you're using the WASD configuration for movement, you have to back your fingers up just a little bit to access the following keys: 'Z', 'X', and 'C'. If you use your first (index) finger for the 'D' key, you have the following other keys at your disposal: 'V', 'F', and 'R'. Adding 'Q' and 'E' to the mix, you now have a total of 8 keys to bind. Along the left side, usable keys are TAB, SHIFT, CTRL, and ALT. Adding in the SPACEBAR, you have 13 keys to use, and if you subtract the ones you use for jump and crouch, you now have 11. TAB is generally used for the scoreboard, and the CTRL key is usually for firing (it's hard to finger in the WASD configuration, too). Few games allow CAPS LOCK for binding. This leaves approximately 9 keys that are available to re-bind for various events. Most of these keys are reached by the first finger, and only one by the fourth finger (shift). You will notice that I didn't mention the 3 number keys; if we add them, it makes 12, but number keys are usually left for switching primary weapon. With binding these keys, your primary directional finger (second finger), would rarely hit the 2 key, since it's mostly moving between 'W' and 'S'.
What happens when we change a few things? Let's use the following keys for navigation: ‘S’ = strafe right (makes sense in a circular configuration), 'X'=strafe left, 'D'=move forward, 'C'=move backward, 'F'=jump, and 'V'=crouch. Placing your fingers on the home keys, your first finger is used for jumping/crouching, the second finger for moving forward or backward, and the third finger for strafing. Keys available for configuration: 'B', 'G', 'T', 'R', 'E', 'W', 'Q', 'A', 'Z', TAB, SHIFT, CTRL, ALT, and SPACEBAR (total = 14). We've already said that CTRL and TAB were generally used for scoreboard and firing, respectively, which leaves a total of 12 keys for configuration. Now, I know that most games don't require 12 keys for binding--except maybe Call of Duty--but it's nice to have all those keys at your disposal, isn't it?
Above the home keys for the left hand are 'Q', 'W', 'E', and 'R'. 'Q’ and 'W' are non-frequent keys, and so they are placed in the upper-left-hand corner of the keyboard. 'E' and 'R' are placed in a spot where they are reached easily with the long reaches of the first and second fingers. Thus, it would make sense to bind the 'Q' and 'W' keys for events that are useful, but non-frequent, like "switch weapon", or "use med kit". Available for the fourth finger are 'Q', 'A', 'Z', SHIFT, and ALT; four keys available for one finger. Granted, they may not be mutually exclusive events on one finger, but if that finger isn't busy for movement, it's easy to hit 'A' to throw a grenade and then quickly to 'Z' to start berserk mode, whereas if you are holding 'W' to move forward and need to press 'X', you're at a loss of movement.
For the index finger, the following keys are at your disposal: 'T', 'G', 'B', 'R', and 'V': 5 keys. Because the first finger isn't exactly used for movement, it's possible to use the index finger for these (many games have option to use crouch (and sometimes, even jump) as a toggle. When using any of those 5 keys, being at a loss of a jump puts a gamer at less risk than being at a loss of lateral movement.
Most people will argue that it's not logical movement for the 'S' and 'X' keys to be used for strafing, and would be too confusing. As I said before, the human brain is a wonderful powerful thing that will easily re-learn these movement keys. Try it for at least a week, maybe a month, even and see how quickly it's learned. For me, being a lefty, I use the following Key setup: 'J' = jump, 'M' = crouch, 'K' = move forward, ',' = move backward, 'L' = strafe right, '.' = strafe left. I now have the following keys at my disposal for binding: SPACEBAR, 'N', 'H', 'Y', 'U', 'I', 'O', 'P', ';', '/', SHIFT, "'" (single-quote), and '[': 13 keys optimized for my gaming. In all fairness, to those that would argue their number keys, '1', '2', '3', and '4' available, I now have '6', '7', '8', '9', and '0'. Game on!