There are lots of other examples on the website. I think to use up-to-date screenshots is very important. They would give new users a better and more accurate impression of Ubuntu compared with old screenshots.
Well with the release of 8.04 would have been good to update the web pages, but since the theme hasn't changed much it really won't make too much deference. Since Ubuntu 8.10 is suppose to have a new set of theme I think it will be a good time to update the pictures on the site.
Yes, when 8.10 comes out the screenshots must be updated, if not updated before that. But I think the screenshots should be updated with every release. Even the theme hasn't changed there should be at least some difference between wallpapers.