Since permabanning someone takes effort and just, you know, avoiding a site doesn't, I'd say yes. There's just not much of an argument to having to perm someone who could just not log in. If that isn't something one can do, then they must not really want to leave the site.
That said, maybe in the future The Mods and Admins could agree on adding a 'Delete Profile' feature.
I actually don't like the idea of deleting profiles. Just opening up old threads and having the OP be "DeletedUser2091" with no avatar would be really sad.