As a few other people pointed out. What I think is that popular stores will get stocks replenished far more often than smaller stores.
If a store sells an average of 100 ps3 a week, they will probably try to get maybe 110 ps3s shipped a week, and then maybe skip a week when their stockpile grows too much. Because it will take up too much space to buy enough ps3's to sell for a month.
On the other hand if a store is only selling 5 ps3s a week, it doesn't make sense to order new ps3s every week. They would save on shipping by buying lets say 30 ps3s a month, and only replenishing their stock every month.
Ofc in the end the numbers will get balanced out by the end of the month, since ps3 isn't shipping more consoles until the next month for small stores, but at certain times, such as when the holidays are approaching and stores start stockpiling more consoles, the ps3 should have a bigger ratio of shipped to sold than the xbox 360 until the holiday seasons end when the smaller stores finish selling their stock of ps3s
This is obviously just my idea on how things are done and not some cold hard fact.
