Most people just really aren't too bright. A lot of times when I'm at someone's house, they've got their wide HDTV stretching out a picture from a normal broadcast because they don't know how to fix the ratio for when they aren't watching HDTV. Some don't even realize that their picture is stretched.
I wouldn't find it hard to believe at all that people are unable to adjust their resolution from 1024x768 or something and therefore end up with everything stretched.
But no, widescreen monitors run at 1280x800, 1440x900, 1680x1050, and things like that.
For games that don't support widescreen, it can usually be forced. I only had a problem with Battlefield 2, but that can be fixed by changing the properties of the shortcut icon.