It's just as easy to get the IP of an unregistered poster. However for an unregistered poster,
anyone can use that ID, since there's no password. So all you really have is the IP for that particular post.
I'm not a big fan of unregistered users, as their posts rarely seem to contain interesting content, and are much more likely to be silly, immature, or offensive. But perhaps it's useful to have an outlet here for that sort of thing (though we're cutting down on the "offensive" part) - otherwise these people would be more likely to pollute other forums with their... well... drivel.