I have a smartphone that is 3.5 years old already, and it's still getting the latest OS updates. It wasn't even sold as a developer phone either. I'll leave it to the reader to guess what phone it is.
No matter how you spin it, Android OS updates are one big pile of fail, even if you buy a Nexus device.
The iPhone 3GS is not quite three years old, and is the oldest device supported by iOS 5. Its predecessor is just under 4 years old, and is not. (i.e. your 3GS "got" the latest update, it isn't "getting" new ones and will be obsolete at the next major revision too). So Apple products are better supported by about a year.
Actually, you can look at this as an aliasing issue in the data. The 3GS and Nexus One were both the "oldest" supported phones at the release of a major OS version, and that happened about just about exactly 2 years for both of them. One fell on one side of the support decision and one on the other.
The "pile of fail" flameage is beneath this site. Stop that, you're polluting our nice community with your garbage. Argue. Don't sling poo.
No matter how you spin it, Android OS updates are one big pile of fail, even if you buy a Nexus device.