This is a pretty shitty argument.
I work on developing web applications and at work I have two 27" 2560x1600 monitors and the advantage of them isn't that I can run webapps in a 2560x1600 browser window but rather that I can fit a browser AND my tools on-screen.
I've coded on "mainstream-sized" screens in the past and it's pretty painful. Want Firebug and your browser window visible at the same time? Gotta shrink that browser window! Want a couple of terminals as well? Heh, good luck with that.
With my current setup I've got plenty of space which makes it working much more comfortable than if I always had to keep moving windows around to show the various things that I want to see at the same time (like say, two different logs in terminals, firebug, a browser window, an editor and finally an extra terminal window. This would hardly be a heavy setup but good luck fitting that on some "HD Ready" screen or even a single 1080p screen).