IMO it has always been a quick trip on a site if I am hit with ads ads and more ads. In the early days before people really knew what these were it was pushed by all of Google. Time has changed people are tired of being bombarded by advertisment when they want information. I know the bounce rate has gone through the roof with muliple ads plastered across the site especially above the fold. I am not at all suprised with this move.
Won't ever happen on Google as would you remove your bread and butter.