Humanity's Little Quirks

Has anyone else noticed that humans are incredibly averse to touching each other? Western culture has desensitized people to shaking hands, but that's about it. Other than that, the only people who actually come into physical contact are young kids or adults in a serious relationship.
Haven't the slightest idea what I'm saying, or why I'm saying it? When was the last time you saw anyone on a street give the half-hug/shoulder-hug thing to someone they didn't know? If that ever happens, there are only two explanations: the hugger is retarded, or the hugger is trying to steal from the hugged. Does that seem odd to anyone else?

Can anyone explain, or even hypothesize, why humans try to avoid touching each other?
I know this is nothing like my typical post, but I have wondered this for a while, and can't find a satisfactory explanation.