I kind of wonder if that's because a lot of updates are rolled out poorly to older devices. On my previous two phones, I've ended up running CyanogenMod or another third-party ROM, even at the same base Android version at the stock OTA updates, because many times even the RC versions run better than what's getting pushed by the carrier. Verizon customer here though, so I don't know if other networks are better about that. I also wouldn't be terribly surprised if that effect (wanting a new phone over an update) is intentional.