Amazon has matched the price on the Xbox 360 version: http://www.amazon.com/Dead-Space-2-Xbox-360/dp/B00309U0M6/ref=sr_1_1?s=videogames&ie=UTF8&qid=1303317448&sr=1-1
Usually when you see a price cut like this at Sam's it is on an open-box/shelf copy. Still a good deal, but once someone buys the single copy that's it.