When you make bold statements you generally have to back it up with some evidence. I find it really hard to believe that anyone has the level off accuracy and speed that you get from a good keyboard/mouse combo.
It is a reason that console games come with built in auto aim on all FPS shooters...
I'm looking for the original study I saw. I haven't found it yet, but here's one that found that trackballs were superior to thumbsticks, even for users familiar with gamepads and not trackballs (hardly a revelation, certainly, but you'd be surprised how many people contest it): http://www.yorku.ca/mack/FuturePlay1.html
But come now, my original statement was hardly all that bold. Obviously the reason that gamepad aiming sucks is just that thumbstick aiming sucks. Replace the thumbstick, solve the problem. (And as a bonus, get analog movement as well as analog aiming--the traditional WASD doesn't allow for speed gradations.) I used to game exclusively with a trackball and never had any troubles. The only reason I stopped is that nobody makes trackballs for left-handers anymore that are any damn good. And if you don't believe me, I just gave you a couple of quotes from gaming professionals.
I'm pretty sure CoD and CS both involve aiming a crosshairs. That's the only thing that's really relevant to this discussion.
As for Starcraft, you're right, it wouldn't work; not because of the pointing device, but because a gamepad doesn't have enough buttons to manage all the hotkeys. In my original post, I called out FPSes specifically for that reason.
It is a reason that console games come with built in auto aim on all FPS shooters...