Yeah, not rude not to post a picture, but pictures can be very helpful for an assortment of reasons. I'm sure some people go to linkedin and disqualify people who are "not attractive enough," but I'm sure at least as many people are just trying to make sure they're identifying the right Sue Baker, as Sharnita put it, or just wanting to put a face to the name.
As an aside, I applied for ~15 universities in 2002, ~10 law schools in 2008, and ~20 jobs in 2009, and none of them asked for pictures. In my experience, many sophisticated employers prefer not to have pictures of applicants because it increases the possibility that somebody can sue for race discrimination, etc.