But wouldn't you agree, that with an average user (which it sounded like the post was about) access to the source code is irrelevant?
Also, people like to play lots of games, etc... Linux isn't undersupported per se, but there just isn't as much support for mainstream products, meaning games, which this AIM person most likely plays.
Also, Windows XP is all-around fairly well done and pretty stable, but I would rather use 2k if I had to choose.