Anonymous, I suspect you're trolling, but giving you the benefit of the doubt I think it's completely false that you need to know PHP, SQL, or even good XHTML to use WordPress. If you continue to post the way you have been under an anonymous account I'm going to moderate your posts as trolls. If you have something constructive to offer, maybe you should think of a better way to phrase it.
Next, to clear a few things up. First, this discussion started around the use of an unordered list for the menu in the admin area. 99.9% of users are never going to change anything in wp-admin, much less look at the code, so I don't see why it's particularly relevant why we code one way or another.
As has been said before, the better the markup is, the easier it is to style things. The more it can be leveraged. The cleaner things are when you need to make changes later. Sure there are poli-philosophical reasons for using web standards, but if those don't float your boat there are hundreds of practical reasons to use them. Ask Wired, Fast Company, ESPN, PGA...