I've pretty much come to the same conclusion as well. I don't have a single friend anymore (its a long story though, not all my fault either). I only talk to coworkers if they talk to me first. I don't actively try to be rude to anybody, i just accepted a long time ago (all the way back in middle school, half my life ago) that i'm not somebody people actively want to be around no matter how hard i try.
I've pretty much come to the conclusion that something must be wrong with me or i must do something everytime i meet people or talk to them that makes them want to just be polite and nothing more and not want anything to do with me beyond that. I mean it has to be something i'm doing, i've always been almost friendless, never dated, and even my own family doesn't want me around unless i'm in school. Its actually a pretty depressing topic. I think it says a lot that i was elated yesterday when my (highly suspected) aspie coworker said thanks cause i took over for him so he could leave for the day. No one ever talks to me so I was happy. I don't take a smile and a greeting as being anything more than that, everyone does it cause its polite, people feel rude if they don't. Save this one kid, but he talks to everybody he's pretty much everybody's casual work friend.