Marvel sues everybody on earth

I suppose it's easy to see this as Marvel just rabidly suing anyone whose work vaguely resembles theirs (a la the "City of Heroes" suit), but I think there might be a bit more to this one. After all, if the only similarity is that it's a school for superheroes, why didn't Marvel go after Sky High, that's coming out later this summer? I think there's a bit more to this one.