There are many situations where you may need/want to wrap the UL in it's own div. This can be related to JS, backgrounds, browser issues,

Originally Posted by Jeff Andersen Negative, all those effects can be done via the UL.

That's not really the case. Suppose you need two images (multiple backgrounds has very limited support), or the UL needs to be floated to the right? Or the UL needs a z-index but is absolutely positioned - in this case you'd need the div to apply correct z-indexing to ie6 which ignores z-index on an absolutely positioned element so the z-index must be applied to the parent (in this case the div).

There are always rules, exceptions, and rules with exceptions for the exceptions