The Delorie one has the problem that it only works if you specifically allow it via a page on the site: delorie.htm must exist in the target site. So, that makes it a bit more difficult to use if you just want to show something to people creating crappy websites.

However, the W3C one has no such limitations, and looks to be generated via the same method, so I don’t think there’s any reason for mine to exist, other than it’s handy to have these things lying around for myself.

(For example, without the ads.)