Well I think you're comments are based on the world before the LCD monitor... And back then I could see your point - now it's imo not THAT valid anymore.
But of course if your site for some odd reason attracts a major procentage of 800X600 users of course it would be stupid not to think about that.
But tbh my comments are mainly based on the fact that I don't like to always compensate for lowest margins...
Actually I think we should design our sites for 1280 and above and just add a sticker saying something like - you are running with a low resolution monitor and that is probably a CRT monitor. For the sake of the enviroment get a LCD instead
Just like a "Get FireFox" sticker
And imo people should actually watch out for sites designed for 800x600... The images you will use for such a site are in some cases so small that the majority of your users will have to leave the site because the "stamps" are dull and doesn't show much