I would like to point out that, perhaps, editors have some kind of 'nostalgia' with their skin, but I also see that editors are not helped when they want to configure or to improve the design of 'their' wiki, and CSS and JS pages have to be maintained by a few admins without an expertise in web design (I'm one of these), with bad results (in other cases, those pages are directly not maintained).
Wikipedia is visually outdated and the success of many companies offering designs for Wikipedia (and mass media announcing these services) makes this problem obvious. But being outdated is not the whole problem.
Why can big pictures on the articles overflow? Wouldn't it be simple to add a "max-width:100%"? Too many failures remain after too many years...