There's no literary term for the quality Twilight and Harry Potter (and The Lord of the Rings) share, but you know it when you see it: their worlds have a freestanding internal integrity that makes you feel as if you should be able to buy real estate there.The word you're looking for is "worldbuilding." It does exist; you just don't bother to pay attention.
Edit, two hours later: What Grossman is ignorant of is the fact that there is an established body of criticism concerning fantasy works -- or, worse, that he feels free to ignore it. Why is it that a writer for something as respected as Time magazine doesn't even realize he knows nothing about his subject -- or, again, feels that he can completely ignore that ignorance?
Lev, this is your homework: get a copy of the Clute/Grant Encyclopedia of Fantasy and look up "Polder" and "Wainscot." Read those entries, and follow whatever links interest you, for at least two hours. Be ready to show your work.