True, and I've heard that iOS 4 didn't run so well on the iPhone 3G in the first place. However, even once support was dropped, the iPhone 3G was still on the current major version (4.3, a relatively minor update, is the version that dropped 3G support), and it doesn't seem like apps required 4.3 until well after that version was out. That's a big difference than being 1-3 major versions behind on Android (especially considering the rather substantial changes in each major version of Android).

If you bought it when it came out, no. If you bought it near the end of the lifecycle, sure.

Supporting phones 24 months after selling them does hold some merit, as that's the upgrade cycle the consumer is contractually incentivized to meet.