Keep in mind that traditionally Warner Brothers and Disney have worked together in the past on countless projects, and the fact that Six Flags and Time Warner are actually trying to cut the ties.
Disney had the chance to actually make the Harry Potter movies... Disney turned it down. Same thing with Lord of the Rings.
And Harry Potter even came across for Disney publishing too... it was turned down as well.
An ex-Universal Big wig once said that Disney had the rights to Harry Potter wrapped up. I find it incredibly hard to believe.
And about the films for the GMR... these are all very short clips... and if you watch it, you realize that many clips aren't Disney or MGM, and of course, Forrest Gump was just added, and it's not Disney. It's not that it would cost too much to include non-Disney clips. Disney just wants to promote their own films over someone else's.
Anyway, thanks for the update BPF!