Like 250 million iOS users out of 365 can't use 2 of the biggest features of iOS - Siri and the 3D Maps (and also turn by turn I believe). How is that for fragmentation?
Yes, Apple does port an iOS version to most devices, and yes manufacturers have been very slow with ICS, but Apple doesn't push all the features when they port the OS to older hardware either, and sometime they are major features.
You have to remember that apple makes software to sell hardware. If they didn't restrict some features to the newest hardware fewer people would upgrade. Oh and the experience may not be as nice...
Yes, Apple does port an iOS version to most devices, and yes manufacturers have been very slow with ICS, but Apple doesn't push all the features when they port the OS to older hardware either, and sometime they are major features.