I think the windows 8 / metro / startmenu thing is like the windows media center but in reverse.
Microsoft said more or less "not many folks use media center the stats show us this fact" but in the last 2 versions of WMC very little has been done to promote it. it's a "Hidden feature" that i bet 70-90 % of users have never even seen and even if they have seen it very few of them have a cable card slot to get use of one of the key features .. or a tuner card for that matter. so now it's going to be an addon for windows 8.
I rather suspect that the folks at MS have a fear that if they did not push metro it would not take off and go mainstream and wind up like WMC soon down the road.
so they "bet the farm" on it.
problem is that for a can't even begin to count how many users the new metro start screen will be a deal breaker as it stands now with forcing it on users.
IMHO they should have just done two versions of windows and let folks pick the one they want.
if metro and the tablet are as great as they think they are the market would show this with the sales numbers.... that's a really good "stat" to go by.
there are problems with the two versions idea yes, but I see problems with the "all in one" method also.