Anecdotally, the place I work has people with wide screen, 19inch monitors that insist on using them at 800x600. It looks awful, but they're used to it being huge, and they refuse to change.
I've seen a few people like that before myself. I think that at least some of them know they can increase the resolution, and they try it, but they switch back before their eyes can adjust.
If they care about user experience, they'd detect the window size, and adjust the ads / layout accordingly. Hopefully they'd do that, but I'm skeptical.