Whatever your opinion of the quality of WB skins, WB has at least demonstrated to MS the size of the customer base for whom GUI quality & functionality matters. That the Windows GUI has had serious limitations in customization is part of the reason WB skins aren't better than they already are. One can argue that it all goes back to Apple, since getting an Apple look on a Windows rig was probably the original driving force behind skinning Windows, but the Windows customization market is huge and now self-sustaining. Microsoft was bound to take notice.
Cheers,
Daiwa