Marketing is not sales. I would like to clarify. I was not saying talking about the ways in which a site promotes itself. People set up web sites to advertise which provides them with value when customers subsequently buy. People charge for access which provides an immediate return.
People sell product which also provides an immediate return.
And, people put information up because they love the subject matter and want it to go up. The Internet provides a rich toolset for inquiry response, consumer education, investor relations, customer support, and much more. It gives us feedback mechanisms which would be far slower and much more costly by other means. However you were right to add two others. Aquisition Technically this is a form of advertising.