Like when the PS2 came out - it's marketing, there is no shortage they are just playing the market.
i heard on the news that the factory over seas that makes them is on the job 24/7 and they still only have about half as many made as they would like to.
also, if they have more, why did you need to order/reserve one and they sold out?
right now it is advantage bill gates. the ps3 and nintendo's next box isnt even out yet so everyone and gary's cabbage patch doll want a xbox360.