Michael Degusta from the understatement did a tremendous job putting together a breakdown on iPhone vs. Android phone device update and support history. [Click/tap on the thumbnail above to go to his site and see it in full.]
Just as LTE-support, user-changeable batteries, different form factors, etc. are legitimate points of consideration when it comes to choosing beteen iPhone 4S and the various Android phones, so is vendor support and their history of OS updates. Not just for consumers, but for developers as well.
Even if you upgrade your phone every year, it will influence your ability to repurposeold device, hand it down, or sell it.
Check out Degusta's full chart and highly detailed post via the link below.
Source: the understatement