Microsoft obviously has struck some deals with pc producers and committed to hold the product back until after the holiday season. They probably even make more money that way.
It's just a matter of time, until Apple is going to counter the Surface with their own ios/macosx hybrid, which I think is the future. I would not be surprised to see the first hint for this "surface" sometime early next year, after the holidays, and before the actual Surface Pro hits the stores.
Microsoft is betting for Apple to not pull this off so quickly, but if they are wrong, the Windows market share will continue to shrink at an accelerated pace next year.
Microsoft had their shoot this Christmas season to do something bold and go big with Surface RT AND Surface Pro, but they choose to give in with the OEM's.