Here's the rub. Blizzard hasn't yet divulged a release date for Cataclysm, probably because they have no earthly idea when it's coming out yet. Until they do, any release dates from stores are, at best, speculation or, at worst, outright lies.
But why would retailers list a release date for Cataclysm if one doesn't exist yet? Simple: to take your money. Many game retailers (Gamestop especially) stock their stores based solely on preorder numbers, only getting a few extra for the teeming masses that never thought to go to Wal-Mart to get a guaranteed copy without putting money down first. In the meantime, you get to ... not have that money. Not a good deal.
Preordering is a process designed to get money from you without getting anything in return for an inordinate amount of time, so wait until Blizzard announces a date before you plunk any of your hard-earned money down. And, again -- we know when the sites say Cataclysm's coming out. You'll know just as soon as we do when it'll actually be available.
World of Warcraft: Cataclysm will destroy Azeroth as we know it. Nothing will be the same. In WoW.com's Guide to Cataclysm you can find out everything you need to know about WoW's third expansion. From Goblins and Worgens to Mastery and Guild changes, it's all there for your cataclysmic enjoyment.