"Earlier this year, Android 3.0 launched with a new 2D rendering pipeline designed to support hardware acceleration on tablets. With this new pipeline, all drawing operations performed by the UI toolkit are carried out using the GPU.
You’ll be happy to hear that Android 4.0, Ice Cream Sandwich, brings an improved version of the hardware-accelerated 2D rendering pipeline to phones, starting with Galaxy Nexus."
Comments
One example from the graphics APIs / changes:
"Earlier this year, Android 3.0 launched with a new 2D rendering pipeline designed to support hardware acceleration on tablets. With this new pipeline, all drawing operations performed by the UI toolkit are carried out using the GPU.
You’ll be happy to hear that Android 4.0, Ice Cream Sandwich, brings an improved version of the hardware-accelerated 2D rendering pipeline to phones, starting with Galaxy Nexus."
http://android-developers.blogspot.com/2011/11/android-40-gr...
You can walk your way from http://developer.android.com/about/versions/jelly-bean.html backwards to see what is missing on older phones.