It is no secret that Google shifted from content-based ranking to link-based several years ago. The way most people discovered this was by seeing their pages disappear from top ten placements overnight. Unfortunately that same lesson is being re-taught today as Google shifts from an “all link”
model of determining popularity to one of “inbound only.”
It should not come as a big surprise. It’s been happening slowly for the past year or so but is now in overdrive. Pages that have dominated top spots for years are suddenly disappearing without a trace and linking is the key. In short, reciprocal links no longer count as they once did. Google expects to see one way inbound links in its top ranked sites. The reason apparently being that worthy sites can attract links without having to reciprocate.