However, everytime people bring up GPU, I call BS. Windows Phones were responsive and fluid with 1ghz cores and Adreno 205 GPUs. You do not need some state of the art GPU to make the UI smooth. Hell the iPhone 4 and its weakass GPU achieved 60 fps smoothness long time ago. It's only recent OSes that have become more bloated show the age of that phone.
Well, I guess it's a free country and you are ALLOWED to call BS; however, you would be wrong.
The issue with Android is that prior to 4.0 (ICS), the entire UI was non-hardware accelerated; meaning that the only job the GPU was doing was actually outputting the frames. With ICS, hardware acceleration was actually implemented into the UI and not just within applications.
IIRC, Jelly Bean and "Project Butter" added support for triple buffering and for vsync to lock the framerate.
Android prior to ICS was using the CPU for rendering. Both iOS and Windows Phone have been hardware accelerated all along.