Citation please? Cannot seems like an unreasonably strong claim.

Given the way older iOS devices are often sluggish on newer OS releases, it seems entirely possible that the animations on the switched-from device were slower and less smooth than the animations on the switched-to device.

Citation? Here, both sides actually:

http://www.inspiredgeek.com/2011/12/07/why-android-graphics-...

https://plus.google.com/100838276097451809262/posts/VDkV9XaJ...

https://plus.google.com/105051985738280261832/posts/2FXDCz8x...

http://appadvice.com/appnn/2011/12/android-lag-attributed-to...

The latest of those citations is December 2011. They may not reflect the current state of the Android OS.

Android 4.1 and 4.2, codenamed "Jelly Bean", have been released since that time, with a "Project Butter" specifically aiming at GUI smoothness.

I haven't had a chance to use anything newer than 4.0, myself, so I'm merely pointing this out. It could be the same for all I know.

Project butter did nothing for the Nexus S, which in my experience has been mady worse with Jelly Bean.