Super hero movies have millions of children begging to go see them. I don't think Star Trek has that going for them (although I did as a youngster).
I think there maybe something to this. My friends who have young kids have seen Iron Man mainly because the kids wanted to see it. Star Wars does well with the kiddies too. Trek audience seem to be older, over 70% of the moviegoers in the opening weekend of STID were over 25 years old.