This is a good point, and one I've addressed before, but here is my understanding. The title has been translated as both "A Doll House" and as "A Doll's House." I've even seen it translated as "A Dolls House," though to me this is the poorest interpretation. In any case, the original Norweigan is difficult to translate and a choice is made on the part of the individual translator.
Your take is certainly valid, but if you argue the other side, you might postulate that the possessive is true, that Nora lives in a superficial, closed world, treated as an object rather than a real person.