Most of the 'ads' in windows are actually just promotion of those services, or content available through those services. It's something that every other commercial OS does with their first party apps - iTunes is full of promos for iTunes content. But an article titled 'Windows 8 is about services' doesn't get as many pageviews as 'Windows 8 is about ads'.
Isn't an app store literally just a wrapper around advertising though. Yes the ads there seem particularly low on instructive content but the rest of Android OS doesn't have advertising like that does it.