I'll have you know mine is just barely over (was too lazy to adjust it those last few pixels)
Seriously though, many blogs are designed to have a flexible width so that they look decent on 800 and up (although perhaps a bit bare at larger resolutions) I usually try to go that route myself and probably will with the new theme I'm working on.
Many mainstream blogs I've come across are either very narrow or adjust to fit so I think perhaps the larger size on adult blogs might be because most of us have bigger screens, and we're also trying to fit alot more images/ads etc on the page.
Personally I would go with a flexible width with the small end being 800, because then it will look decent to most surfers.