Look at it this way If they clear up everything that happened in X3 in DOFP than X-men 3 looks alot better in the Box set, and in the overall story of the franchise.
because if people don't know that much about X-men they can get a Box set with X3 and First class to get them ready for DOFP, or after they watch DOFP, they go back and watch the last two movies.
Sort of like the Star Wars episodes. So it a win-win for X-men films.
