are you sure that you dont get aim assist on pc gamepads?
Sure there is, its called aimbot. All the "good" players have it on Bad Company 2!
But in all seriousness, most console FPS have aim assist. Like everyone else said, just try to play mulitplayer with a gamepad on PC and see what happens. But I think gamepads are great for other games on PC. Playing sidescrollers on KB is not fun.