Why?
Why not?
There's been much discussion on this in the ipad 1 or 2 and motorola xoom threads.
Basically, if you want the Apple OS, you go with the Apple. If you want a 10.1" running Android Honeycomb, you can choose between the Xoom or Iconia (and maybe others by now). If you want the Transformer (which I did), you'll have to wait until supply catches up. Which I didn't.
Other tablets by other manufacturers are on the way, as well.
As far as I can tell, everyone is very happy with their tablet of choice.