That is, only elements of equal standing should be together in the same level. Also, a bulleted list with only one item is tacky. In the early days, these and bullets were about all we had to work with, so they got overused, to say the least. In a way, bullets and horizontal rules are cop-outs. The same effects of separation and emphasis can be achieved simply by the proper use of white space.
White space is used to separate elements, and to draw attention to elements, among other things.
It would look neater and more elegant. Alas, traditional HTML gives you limited control over white space. Style sheets and the absolute positioning available in HTML 4.0 however, make the future appear whiter, so bullets and horizontal rules may be on the way out. White space can not only separate elements from each other, it can call attention to a particular element. Perhaps no typographical issue is so controversial as how to delimit paragraphs.