Hmmm, the best I can see is breach of contract, but even that would be tenuous in court since I doubt hasbro could prove that some copies getting released early caused some sort of monetary damages. I'm willing to bet that buy.com may get a stern talking to. At worst, Hasbro could say "We aren't going to sell you any books in the future", although fat chance of THAT happening, it only hurts Hasbro.
The whole harry potter getting released early thing was hilarious, as Rowling's people made all sorts of outlandish claims that were downright silly. Release date is a pure contractual business between distributor and publisher, and there is nothing beyond that that would hold in any legal sphere IMHO.