Ahhh, perhaps that's the difference. I didn't receive a digital copy. I received a coupon to download one somehow.
So does the digital copy you received work in iTunes?
I'm not sure, I haven't tried it yet. I got a digital copy with The Nightmare Before Christmas and it worked in iTunes. It works the same as if you bought the movie off of iTunes. You have to authorize it and junk.
That's why I usually do it myself with Handbrake because then you don't have any limitations.