Looks like google was cleaning house with sites that used hit-counter services to embed links. I am seeing the same thing for other markets/industries where sites used similar strategies.
BTW – The sites arent totally gone, just bumped down to page 5+, so it looks like there were penalities, but not outright bans.
Google seems to be making a real effort to identify sites that are gaming the system these days so I wouldnt be suprised if there were some major serp adjustments in the near future. There have been at least 4 sites that were page 1 for “online casinos” that were hit hard in the last few months and all the affected sites in some way, big or small, violated googles backwards-ass terms.