Of course, we're still talking preorders here -- just because they got reserved doesn't mean that they'll all be sold, so there's still a chance that you could get one at release (Gamestop, we believe, will hold reserves for 24-48 hours after release, and then sell them first-come, first-serve). And there's a chance that Blizzard could put a larger order in (since the game hasn't gone gold yet, the sets aren't even manufactured yet), which would mean more preorders would be available.
But on the other hand, Blizzard has always wanted the Collector's Editions to be limited, and the guys at Gamestop assured us that there were still plenty of regular copies to reserve. It's hard to believe the CE could be completely sold out in just two days, two months ahead of the actual release, but it's clear that Wrath is going to be one of Blizzard's biggest releases ever.
Update: And now, for some reason, it looks like preorders are back up. Either Blizzard decided to make more or Gamestop figured out how they could sell more, so if you want to get one, better order it quick.