I was looking at W3C's Techniques for Web Content Accessibility Guidelines 1.0. Checkpoint 14.1 says
14.1 Use the clearest and simplest language appropriate for a site's content.
When I read that, I realized that I've been doing it for some time, almost subconsciously. Not just in web pages, but in email, on irc, anywhere I write something that could be read by a non-native English speaker. Which is important to note, I think. Dumbing down, at least when I do it, is not really for dumb people, it's for people who don't know your language as well as you do. After all, why should they know it?
Sometimes it's painful when I want to turn a phrase in a clever way, but don't because people might not understand. But it's better than confusing them, especially if I'm trying to help with a programming problem or something. Simple language is not usually something our culture values. But maybe it should.