I have always thought this was not only a product of the frequency the right-hand column is used only for ads, but also the ways in which people consume content. Specifically, people in the Western world are used to consuming content from left to right. With a large left-hand column full of content, users will begin consuming there. This makes them much less likely to move to the right-hand column, which usually consists of (if not ads) supplementary information to the left-hand column. For instance on StackExchange, where it is full or related links, etc. for further reading.
Because of this, my thought has always been to either a) make both columns of equal size as to emphasize both equally and force users to choose either to start with instead of defaulting to the left, or b) remove the smaller right-hand column in favor of a small left-hand column and a large right-hand column containing the bulk of the content.
As an exercise, think of the ways in which you would browse StackExchange if the right-hand "Related" and tags sections were on the left-side of the answers, and there was nothing to the right. It may not change the way you use the site any (functionality would be no different, after all), but it, in my mind at least, changes the way I look at the articles, and the way that I would seek to supplement the current answer with additional information, as well as what my eyes would come into contact with first upon page-load.