They don't have time for that. Now there is only iPad with significant sales number. In 6 months Android tables will start to sell in significant numbers.
In 12 months opportunity to conquer world market with new tablet OS will disappear.
If Microsoft thinks that it can release a product with software that's not ready for release on just price parity with the market leader, they're delusional.
Apple spent the better part of 2011 (ie, last year) proving that iOS doesn't need a daddy OS around anymore - why is a USB host feature in a tablet meaningful for users? So that I can upload my picutres? Why not I just stream them to your photostream? or push them into your google drive or dropbox?
History repeats itself faster than ever.