Given that some local authorities only migrated TO XP in the last 18 months or so, and that even the most forward thinking businesses are still qualifying W7, it may well be that Redmond expects big business to move to W7 after XP, and take 3 or 4 years about it, by which time the tablet wars will be won (or lost, supposing they even start. I reckon MS is too late to that party by a generation).
The natural path for Corporates is XP -> W7 sometime in 2014, then W7 -> W11 some time in 2022.
The success of W8 will not matter in the corporate market. They are not going to up sticks and go to Linux (much as I wish they would) because of W8. They will just stick with XP then W7.
Microsoft is, I agree, looking like someone taking very careful aim at their own foot. But to shoot themselves in the other one they would have to prevent corporations migrating to W7 for the remainder of the decade, and past history suggests they won't do that.