Well, the way I first learned about this font rendering was while I was toying around Metro apps - Weather, News, Sports, Trending, etc.
The text was pretty bad in metro apps. To make things worse, a lot of metro apps eventually redirect you to Internet Explorer. (e.g. MSN News, Bing search, etc.) That's how I noticed something is not right.
As for ClearType tuning, I do it on every Windows OS to my taste. But according to Rhonda the Sly's link, ClearType has no bearings on Metro or IE, so that's pretty much explains it, it seems. So basically this is another Metro (and IE) thing, and doens't affect other "legacy" applications.
P.S. According to Rhonda's link, MS expects higher DPI/PPI displays to become popular in near future, thus negating the necessity of better (existing) font rendering. I wonder how that holds true on desktop considering Metro UI and contents (linked to IE) look pretty bad on my 30" (2560x1600) display, which already has pretty high DPI/PPI for a destop monitor.