First off, why would you want to build content-rich websites? The short answer is "Because it keeps people on your site for awhile, it makes them come back, and they tell their friends about that site."
                 But why? Well, for one thing, people will stay on a content-rich site because it takes awhile to read an article or two. Thus, while they're reading the material, their peripheral vision (off to the sides) notices little ads that happen to surround that articles.

                  And if people start to realize that a certain site has good content that they like, and in particulat, different content that constantly changes and is updated, then they'll check back to see what's new.
                  The worst thing in the world to have is a stagnant website that never changes. people will visit it exactly twice-the first time to check it out, and the second one to see what's changed-and when they find out it hasn't changed, they most likely won't come back. Ever.