While Android might be internally consistant, the hardware drivers that support it isn't. Everywhere your software interacts with the hardware is suspect for fragmentation. Google will have compliance testing to force OEM's into correctly supporting the Android runtime. However, their only leverage is the inclusion or not of their Google Apps and the "Made with Google" logo for the back of the device.

The handset makers (mostly HTC) have taken to shipping the same kind of "value add" UI changes that they did with Windows Mobile.

What's most unfortunate is that it's not even bullshit -- they are actually adding real value! HTC's on-screen keyboard is better, and they add in some of the multitouch events that Google foolishly left out.