Not coding for 800x600 in these days of high resolution, high-bandwidth design, is a logical tradeoff.
For whom? You? Or your client/employer?
There are millions of people, credit card in hand, who will just click somewhere else if they have too much trouble with your page.
My clients don't want to leave a single penny on the table. They're the ones who determine the tradeoff, not me.
For what it's worth, in this completely unscientific survey, much less than 1% of all visitors to my site use 800x600. There are 15 more popular resolutions ahead of it. In fact, twice as many people show up on a mobile device with 396x320 resolution (aka iPhone).
- Your app should work at any resolution - Your app should work on any browser - Your app should work on any platform, even grandma's old PII running Windows 98 - Your app should work on dialup, and be sexy for broadband - Your app should be accessible to the blind - Your app should not break when new browser versions are released
...and so on and so forth.
I am perfectly willing to write such a beast. Are you perfectly willing to pay for the hundreds of hours it would take to do it?
Every app designer is unfortunately forced to make some tradeoffs. In some cases, they make many tradeoffs, usually because nobody's willing to pay them to meet the needs of every user out there.
Not coding for 800x600 in these days of high resolution, high-bandwidth design, is a logical tradeoff.