I suspect RROD / QA related issues going on here.
There are several things to consider. Imagine that MS decided to fix its manufacturing process to get rid of the errors and only had hundreds of thousands of units stockpiled + in supply chain. The supply chain for a console selling 150k/wk world wide wouldn't be nearly as stuffed as Nintendo's, for example, but there'd still be maybe two weeks worth of consoles in that chain.
MS recently improved the speed of its warranty-replacement service to about 1 week from about 1 month. They may have injected some new consoles in the chain to do this. They've done it before.
If MS took its production facilities down, which is the only way they could possibly have a shortage for over a month when selling at one of their slowest times of the year, then they're probably working more diligently then they have so far to fix the 3RROD issue. Logistically, it makes sense for them to do this now. They may have determined that letting the issue slide for this long was a mistake and they wanted to fix it as soon as the holiday season was over.







