I have often worked alone, but not always. I've never worked in a pair programming shop, and I would probably find it distracting for anything but debugging or syncing up. The trouble is that complex programming tasks usually have the nature where communicating the ideas takes longer than simply coding them. You'd spend all your time syncing state between you and the other person.

But I don't think this explains the bias. I'm not really sure where it comes from but I found it interesting.