I don't think they really cared that much since it was just a short film they put online. They were just appropriating the music score for something new.
To each his own. Glad you enjoyed it at least. I thought the story wasn't bad, but overall I thought it was very poorly executed. I hope Phase two will include a Punisher film.
I think X-Men: First Class was really good, but I don't think its nearly as good as SM2. I think if any X-Men film should be compared in terms of quality, it would be X2: X-Men United. All great movies though.