How many of us have them?

Was thinking about this after a girl I've worked with for 6 months gave me a hug last Friday because she was going on holiday for two weeks. Then she made a big thing about everyone going for a beer to 'see her off'. I didn't because...
a) It's only two weeks
b) She's just someone I happen to work with

Then it occurred to me that she doesn't have a lot of friends outside work, and that she's not the only person I know like that. I went to a wedding a few years ago of a girl my wife used to work with. Half the guests were from her work. My wife had worked with her for a year and was asked to do a reading and organised the hen do. Since leaving that job, she hasn't seen or spoken to her. Not once in 3 years.

Does your office have people like this? Are YOU one of these people? Am I being weird for finding it weird?