Preinstalled consumer machines are not sales from a demand perspective, only from a shipping perspective. Granted, MS pretty much can count them as "sales" if they want, but it's not as if 180M licenses were actually sought out by anyone.
More telling is the institutional take rate. In the 18 months since release, I have encountered no corporate or edu's among my clients that have chosen Vista, other than one or two workstations for evaluation & testing. Most of them went through bulk purchase cycles in that time and have steadfastly chosen to purchase XP preinstalled, or have forgone a hardware upgrade altogether, choosing instead to wait until they can actually not lose productivity fighting a NRFPT OS.
For me, there's no compelling improvement in Vista, as essentially the entire list of major framework improvements were all tossed long before release. I have greater hope for Windows7, I really do.
Organizations (especially large ones) take a long time to change. My company took 3 years to adopt WinXP from Win 2K. Just the way it goes.