Whether or not some identifier is a 'name' depends more on how you use it than its own structure. For those of us who use URNs, probably. But we're not going to make a huge stink about it. They're all URIs and thus exist in the same 'layer' of the web and have the same very basic semantics. I could name all mailboxes using social security numbers but that creates yet another process of a lookup that you have to go through.
URNs do more than that.
For example, we're setting up a URN based service called a Personal Internet Name which is a permanent name for a individual or organization. And that's why we have URNs.