Key difference is you don't get the mostly similar 3 iPhones - you get 4 vastly different phones with meaningfully different feature sets - and they are even made by different companies. Way more variety and choice.
I bet all of the Google Play sold devices would see at least 2 major updates. (My Gnex got 4.1/4.2/4.3 - and unlike my iPad 3 ios 7 update, it actually got better at every update.) That's good enough for me considering that Android updates are really not the same as iOS updates - most apps including the Keyboard get updated independent of the OS.
How many of those phones can you update in three years, like I just did for my iPhone 4? (An armless man can count them on his fingers? :-) )