Well, maybe look at the protocol. It doesn't strictly prevent ads, but it makes it a lot harder. And for example since there is no JavaScript, there is no way

Well, maybe look at the protocol. It doesn't strictly prevent ads, but it makes it a lot harder. And for example since there is no JavaScript, there is no way to pop open another window, or freeze up the page loading an ad. In fact, most clients don't even display images inline, since images aren't part of the spec. There are no cookies for tracking because there are no cookies.