Well, nobody forces you to upgrade the Touch.
The Touch is very similar in capabilities to the iPhone so each upgrade does indeed offer new functionality that the more basic iPods can't have (or at least Apple doesn't see a need to offer upgrades for them since it's more profitable for them to have people buy a new model instead). I'm guessing that since you pay more for the iPhone in the first place, the updates are "free", while the Touch is cheaper so they try to get more money out of you.
I don't like it.