I hardly put my hand on the mouse while I'm fighting, and that's the only time I can think of where time is important. I have to agree with the previous post, doing so would not only be lazy, but also pointless - first, you have to replace already used keys, which would complicate matters. Second, it'd change virtually nothing. It has nothing to do with the usage of the mouse whether you press up or w, right or d and so on.
