All White Cat is saying is that the wikipedia needs markup(s) to handle dates. And in fact, right now there are multiple markups available, including American-style ones.
Thats not mark up, what your describing is style/layout. The markup would be the wikicode surronding it it.
For example it would be nice if we had a custom markup for date that didn't link it, that could detect what was contained in it would be nice and used the users perfernece for formatting first then fell back to something else like the browser detection or a decided format (at the moment it would appear to be American Dates). I'm talking about something like <<DATE>> and then it would do autoformatting of the date and it would also assist in the metadata contained in the page as well, and also have the ability to force a certain style and define date names as well (eg: <<2008-12-25|f=Friday, 25 December 2008|name=Christmas Day (2008)>>)