I suspect that story had a lot to do with prank celebrity accounts etc stirring things up and very little to do with event invitations being public by default. I'm pretty sure you could achieve similar results by publishing a private email (or paper) invitation with a call to action somewhere like 4chan. I'm also equally certain this doesn't normally happen with the millions of other small personal events that have been publically listed on Facebook.
It's easy enough to point fingers at a company with as little apparent regard for privacy as Facebook, without searching for non-issues and exceptional cases to be outraged by.
