I think your just young and don't remember when 800x600 was considered a good resolution. Believe it or not, at one time the vast majority of people used that res. I remember when my dads business got a 'HUGE' 15" monitor, running 800x600 almost made me cream myself
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But really, there has to be a 'standard' set somehow. Many sites, if they are catering to a technological audience can get away with something bigger, but for most sites 800x600 is still a good rule of thumb.
Many older people use it. It is easy on the eyes and can run on virtually almost any computer these days.
cheers