I think one problem I that there are de facto fanclubs. For example, I'm guilty of voting almost all stories of the sites
http://www.kalzumeus.com (patio11) and
http://www.righto.com (kens). When I see on of them, I read them immediately because they are almost sure good and then I upvote them.
I don't have the data, but probably most programing languages have a set of users that is very interested in them. IIRC this caused a few times a false positive with the voting ring detector a few years ago.
Probably, YC has a mix off many happy alumni here and many fans, so any story about YC get many upvotes fast, and that may look like an artificial bump.