1) Backward compatibility with HTML level 2. If we remove OL, UL, and so on,
HTML level 2 pages will be incompatible with HTML level 3 browsers
2) The Ordered List, Unordered List and Definition List elements really do
represent different document structures. They are not simply differently
styled presentations of a simple list of "things".
3) If doesn't actually simplify HTML at all.
To illustrate the latter point, consider the example of a recipe. This would
typically contain two lists, one an unordered list of ingredients, the other
an ordered list of instructions. Let's assume that for some reason the style
sheet is not accessible, so the browser doesn't know which presentation style
to use for each list, so it defaults to either ordered or unordered.
If it defaults to ordered, then it will put sequence numbers on the list of
ingredients, which might be OK except that it implies that there is some
importance to the order the ingredients are listed in when there is not. This
could be a source of confusion.
If it defaults to unordered, then it will omit sequence numbers on the list
of instructions, which would be very bad, because then the reader would be
unaware that the order in which they perform the instructions matters very
much.
A document structure markup that clearly differentiates the various kinds of
lists is a necessary part of HTML.
Michael Johnson
Relay Technology, Inc.