Depending on the font size, 600px gets you pretty close to the ideal of 50-75 characters per line: http://baymard.com/blog/line-length-readability

Nope. But I am reading it on a 1280x800 tablet in portrait mode. Or I have two side by side 0n a 2560x1440 monitor (effectively 1280 px wide each). Or even worse, two side by side on a laptop with 1920x1200 (960 px wide each). 600px makes all of the above scenarios doable with reasonable margins and other layout items like a navigation menu and ads.

> 600px? Are you using a 1024x768 monitor from 2000?

Why do you think they call it "newspaper column" and not "newspaper spread"? It's because the best way to read is in a narrow column (1/3 ... 1/2 the width of the screen). Otherwise the eyes need to move horizontally too much and risk losing position.

You are aware that we have multi-tasking operating systems today?