Perhaps the most interesting thing I noticed when I saw BvS on Friday was the diversity of the crowd. And I am not just talking race, although that was also diverse. I am talking the age of the crowd. It ranged from about 10 to 70. I saw more than a few older couples (and when I say older, I mean 60+, me and my wife are 40 so are old to plenty of you I imagine).
And that really comes down to one character and one character only. Superman. He is pretty much the oldest comic book character there is, so you literally have generations that have grown up with him.
Include Superman, and it does not matter if your movie is awful, people will go to see it. His staying power is pretty damn remarkable.