its not really a matter of how big they look. (even tho every icon looks like a giant elephant on 800x600)
Its more about the wasted screen space. 10 icons take up half your screen. you cant fit as many windows. and dont even get me started on webpages. OMG, you fit like a fraction of the page on the screen at a time... read a sentance scroll. read a sentance scroll.
i cant imagine these forums on that resolution. one word takes up a full page.
Not to mention the higher res you go the more sharp and nice everything looks.
*switches to 800x600 just to take a look*
WTF, screens all white. nothings showing on it.... Oh!! damn, that was just my mouse curser takin up the whole screen.
:P