Windows 8 faces a number of hurdles in the enterprise, but the biggest reason it won't replace the current corporate champion, Windows 7, is simple: IT shops don't think it's worth the upgrade hassle.
Not worth the Retraining costs. Not worth telling every user that their computer and their desk must only work like Steve Ballmer's, that User Customization is forbidden by Ballmer & Co. Too bad because Win8 has some useful OS changes, but those changes are minor compared to lack of every user's loss of productivity.