While I think there is a bit of marketing shenanigans in the "hurry up before we're out" it is close to the truth. For one, half their stock pretty much has already sold in the first 25 days and the rest of the month is the hardcore holiday sale season.
Also, the hurry up before we are out applies more to retailers. Many retailers will run out (as happened during thanksgiving) even if Microsoft is not out.
Also, Microsoft has done the opposite of artificially creating demand by having low quantities - they have ramped up production and changed their forecast for more sales. I seriously wonder if many of you have any idea how the business world works. Yeah, MS is going to pay hundreds of millions to advertise and is competing with the Sony Move and the Wii and they are going to short supplies so customers buy their competitors products...that makes a ton of sense. Even Nintendo said they should have ramped production up for their Wii; they admitted that the Wii constantly being sold out generated buzz but ended up forcing consumers to buy the Xbox and Sony.