I don't doubt Win 8 demand is "weak", but I understand that app store activity for paid apps more than doubled after Christmas. So I suspect that a better measure will be to see where we are in January after all the folks who got new PCs and other Win 8 paraphernalia begin to be counted.
Not to mention, unlike the reaction to Vista, I don't hear folks asking for their machines to be retrograded. IOW a reaction of - I may not hurry up to upgrade, but I'm also not going to go out of my way to avoid it.
Obviously just my .02 on the matter.