This is done to foil users who exit the site. The effect is that when the user leaves the site a window will pop up in a last ditch effort to grab their attention. This is infuriating. Needless to say, most people will avoid that site in the future. The 28.8 modem speed still prevails and time is precious.
Long lines are tiresome to follow and readers lose interest.
Wider margins or columns would break up the monotony. Each time a line ends, the eye searches for the beginning of the next line. This tiny task is easy with a justified left margin, but if the eye doesn't have that constant reference point it can be distracting. This can disrupt the flow of thought you are trying to establish because the user has to decide whether to follow the link. Let your bold be bold and your caps be caps.