When I see a company say "This game/movie/market item is *only* available here", then I know that it's in real financial trouble.
Today's example: Blockbuster. They are now offering the movie 1408 *only* as a rental through Blockbuster. As it turns out, this isn't accurate (it's available through Netflix, their main competitor right now).
But I always hate these moves. Instead of competing based on how good their service is (and people I've talked to say that Blockbuster online system really stinks, though it's getting better), once you start the path of "Oh, well, we made a deal, and if you want X, you have no choice than to deal with us" - that's when I know they're in financial trouble.
If you can't compete off of value, don't try to get my money by making yourself the only way I can get to something. It's the reason why I never bought Chulip from Gamestop with their "only *we* are allowed to sell this game - suckers!", and it's certainly not going to make me rush into a Blockbuster any time soon.