800X600 WAS a standard, came out when SVGA was introduced and the old guys used 640X480, that was what, 1993-ish?
Since 1995 or so 1024X768 was becomming standard, it is the default setting for 17CRT which is also a standard (low-end) setup today. I was running 1600X1200 back in 1995 and would agree that I was a small minority then, but less of one now. The 1920X1200 I am using now is on a laptop for crying out loud. But with 19" CRTs and LCDs I would say 1280X1024 is about to pass 1024X768 as "the standard".
I think that most webpages use 1024X768 though, the ones using 800X600 are antiquated to say the least.