First, holy crap, I hadn't been to http://www.w3.org/ in a long time, and it looks like they've actually made it to the 21st century!
Second, perhaps cool URIs don't change, but it seems like http://www.w3.org/Provider/Style/URI.html is kind of an unfortunate URI. What's "Provider"? Why are "Provider" and "Style" uppercase? And what's wrong with 301 redirecting (don't break old URIs, but still restructure them as your website matures and you realize a better organizational hierarchy)?
Third and perhaps most importantly, this all seems like a pretty awesome problem to have! How many websites survive more than a few years? (Geocities doesn't count.)
They're uppercase because they're uppercase. Asking why is like asking why Rubyists like_using_method_names_like_this and .NET devs LikeUsingMethodNamesLikeThis.
Oh, and I am not a Ruby developer ;-)
As for a zigzag effect I think CamelCasing is at least that bad, maybe moreso.
Wondering if I get points for bringing early Medieval history into a discussion on coding conventions ;-)
word+empty-space+word
but
word+line-down-below+word
so your eyes go zig-zag from the taller glyphs of the word to the low glyph of the underscore (vertical zig zag motion), instead of jumping to the next world (horizontal).
Searching for the source now.
It's because it is a part of a collection of numerous pages named "Putting Information onto the Web". Its audience is obviously (content) providers, which the URI reflects.
Take a look at w3.org/Provider and w3.org/Provider/Style. It's actually a well-constructed URL. It appears to be a "Style guide" for "web content Providers."