Are you telling me that all those great works of art you just mentioned were created, in the end, because the artist wanted to make MONEY? Orson Welles made Citizen Kane purely for money? Come on, dude, I know you have more faith in artists and the creative mind than that. Sure they make money, but that's a side benefit from the creative process - ask any struggling musician, because 99% of them never become rock stars. Dark Knight you might actually have a stronger argument - is Christopher Nolan the type to take a big budget superhero movie because it'll make him some big bucks? Maybe, but that's not the whole story. Ultimately, he wanted to make it because he liked Batman. Lots of people like Batman because they've grown up with the character, he's a cultural icon, and therefore lots of people will want to see movies about him.
Even I forget this sometimes because we're all so used to the commercial film industry as it exists today, with mass marketed summer event blockbusters that provide the lion's share of profits for the five or six corporations that control the major film studios. But the fact is, people will always want to be entertained, and even if we were living under socialism, movies about Batman would get made because the people want to see them. What's more, they wouldn't be tied merely to crass considerations of box office grosses. Superman, Batman, Spider-Man, all the great superheroes are now cultural icons and as subject to respectful film treatment at this point as any literary masterpiece. I think that would be the case regardless of whether we lived in a socialist or capitalist society (there's a lot of great Soviet movies out there). A proper socialist society wouldn't be totally alien from what we have now; it would develop on from that.