The people who do the marketing are different from the people who made the actual movie, so I thought there was always a chance they could have decided it would be helpful to sales to make sure people know it was an X-Men movie.But if they downplayed it in the actual movie itself, why would you expect them to do otherwise in the promotion for the DVD?
Thinking about it more now, I guess it would probably be the other way around. If the movie itself down played that connection, then they're probably going to avoid it even more in the marketing, since they obviously don't want it to be connected to the other movies in people's minds.