Heck, if it came out today for the very first time, but played out exactly the same way as it did when it first got released, would it still make over a $1million domestic? The quality of the movie, story, and acting would be equal, but if it makes much less, then there would HAVE to be other factors in how much money it made back then.
Heck, case in point, look at E.T. I consider it to be one of the best sci-fi movies ever made, and made tons of money when it was first released. It was rereleased a few years back, and it barely made anything in the theaters. Some of that could be that people have seen it already, sure, but there was a lot more to it than that.
Anyway, GWtW is an incredible movie, and I agree, it will probably be remembered long after Dark Knight is forgotten as just another summer blockbuster, but if that same movie was released for the first time nowadays, I highly doubt it would be considered quite the masterpiece or talked about as long after as it had by coming out when it did.
And it managed that because, among other things, it was one of the first of its kind (particularly in the quality of its storytelling), and because the market wasn't saturated with similar movies. It had the freedom to make its mark the way it did. But with all that said, it's still an incredible movie as far as I'm concerned.