I thought no vanity URL's had something to do with their privacy policy:

> If you choose not to have search engines index your profile, your profile itself won't appear in Google search results. However: * Your profile will still remain visible to anyone with your profile URL.

From: http://www.google.com/support/profiles/bin/static.py?hl=en&#...

If we all had vanity URL's that spelled out our name, our private profiles could be accessed by just guessing the URL.

Now your private profile is only visible to those that know your specific URL and Googleplus ID.

I also think vanity URL's, name changes, name squatting and celebrity verification is too much manual work for Google's liking.