The problem with that is now you have to be careful about touching the entire top of the mouse. You can no longer grab the mouse at any position, otherwise you might cause unintended actions. You now need to put in extra effort to control it.This is literally the reason I like the Magic Mouse. It is so sensitive that I can just touch the top with one finger and comfortably scroll through webpages. The feeling of swiping on the Magic Mouse is what makes it magic, and I far prefer that over any scroll wheel. It just needs more gestures.
It's what makes bad UI, like touch-screen car controls for the AC, where you now have to look at the touch screen instead of looking at the road.
That extra effort to control it is wasted effort.