Cool URIs Don't change
w3.org
w3.org
I think that giving "things" a name is one of the hard problems that programmers tackle every day. Normally our success or failure at choosing good names is kept hidden, and can only be seen by those who look at our code. Websites are one of the rare places where the world at large has to deal with our mistakes.
"Apply this change to the entire freaking internet?" y/N>
If you send someone a content-negotiated URL you can be pretty confident that they'll see the text/html (or application/xhtml+xml :-) version).
Similarly, any typo report more specific than "there's a typo somewhere at this URL" will tell you what you need to know.