we use it? Because we want a mark-up that is easy to read, easy to understand, easy to type and non-intimidating for people who know next to nothing about HTML. When people see lots of nested tags such as on
http://www.wikipedia.com/w/wiki.phtml?title=Duesseldorf&oldid=131461
they are not likely to add anything to it. On this page the mark-up has been more wikified and if you now look in its edit page you will see a text that is a lot more editor-friendly.
-- Jan Hidders