No matter how you spin it, Android OS updates are one big pile of fail, even if you buy a Nexus device.
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.