I agree with you that you're technically right about this. Just because the back doesn't pop off, that doesn't mean the battery can't be replaced. It certainly can by someone with the right tools and a bit of knowledge.
Unfortunately though, this becomes the exception, rather than the rule. As a result of things like this, a lot of perfectly good phones get tossed, when they could easily be recycled to friends and family members. Maybe I care a little too much about our environment, but to me, this is just not good for anyone. :\