Should we compare the percentage of macs running OSX 10.8.5 against the percentage PCs running windows 8? I think fragmentation is just the nature of a distributed hardware environment. I'm not sure what that means really, but there seems to be parallels here.
Windows 8 has been polarising and comes at a time when PCs in general has seen almost no growth. You are better off looking back at the Windows 95 days. In which case Microsoft allowed OEMs to customise parts of the OS whilst still allowing updates.
Google has just poorly designed Android. End of story.
I'm sorry, I fail to see how Android is designed has anything to do with carriers not updating their specific hardware's OS version. My devices are kept up-to-date quite nicely, so I guess Android on those is the one that Google designed correctly?
That's more about Google's negotiating capabilities with the carriers than how they design software.