Here is the thing, they can have the GPU do some of the work and use hardware acceleration. In that case it is just the GPU taking the load off of the CPU's shoulders and carrying it the same way.
However, the iPhone is so smooth because it uses OpenGL to do things. The GPUs in these devices support OpenGL and hence have a bunch of different built-in functions that they do really well. So what Apple may do is instead of just telling the CPU to scroll a screen left, or telling the GPU to scroll a screen left, it actually renders that screen as a texture, and OpenGL can then majestically use one of its functions to smoothly move it left or right.
It is clever use of the GPU and OpenGL that enables iPhone to be so smooth. It isn't simply taking the burden off of one processor to give to another, it is completely changing how that effect is done.
So for Android to do those things, they need to rewrite some things. I think most if not all Android devices have a GPU that supports OpenGL on some level, it is just Google deciding not to do it because it is too complicated or takes too long.
Palm doesn't do it either. Neither does Windows Mobile or Blackberry yet. iPhone is the only one that has committed to it.
