Why hasn't Apple made a touch screen iMac?

Ok this seems to be an obvious... slap in the face one ... but Why hasn't Apple made a touchscreen iMac? Or MacBook even? Everyone else is creating one ... but Apple hasn't. Are they afraid it will dip into their iPad market? Im constantly touching my screen while I look at things on my laptop ... would be nice if I could click or swipe while i'm already there. It seems if you have pretty much perfected the interface of touch screens - you'd incorporate it into all your devices.

I would LOVE my MacBook to be able to have touch screen capability. Sure I wouldn't use it for everything ... but it would give another dimension to my product. Now if they came out with an iMac with touchscreen ... I'll be the first in line. That way you could really put away the keyboard and mouse and just have a nice display on your desk.

Come on Apple ... you are supposed to be leading the innovation ... not following it.