Part of the promise of a theater is a movie before it's on DVD or streaming, and for most people the picture and sound is perceived to be better than what's in their home.

I think the assumption is that movies on iTunes are not available on day 1 of theatrical release and that you don't have a 70-foot TV. Standard movie ticket prices would indeed be too high to bear if the movies were all long gone in other theaters and you watched on a 32-inch screen.