>> Consider why newspapers are written in columns rather than across the entire page. Or why the text block on this site is only 600 pixels wide.
Why are multiple columns not preferred on the web as opposed to wasting half the screen space. I guess there may be issues with scrolling but those should be solvable.
1. The web has its origins in the world of research and academia where most publications have at most 2 columns and usually only one. The current "newspaper/magazine" trend and the challenges associated with it and large display sizes are quite recent.
2. In the early 90s, the average display size was 800x600. At that size, a line of text set at 14px contained roughly 100 characters. Nobody really felt the need for shorter lines. Besides, newspapers don't lay out their content in columns because of legibility concerns but because it makes cutting and moving (parts of) articles easier an improves the general flexibility of their composition. And that's good for advertising, too.
3. Back to the origins of the web, one of the main design goals of its creator was to create a medium that was as independant of the client as possible. From that point of view, columns seem to be quite difficult to execute well. But of course, most of today's web doesn't really fit in their original view.
Why are multiple columns not preferred on the web as opposed to wasting half the screen space. I guess there may be issues with scrolling but those should be solvable.