I would love to get the admin's opinion on this (although not sure if they can share it unless they come together and make a decision together). I for one kind of like the invite system. It isn't impossible to register without an invite from a current user, and invites actually help avoid having people join for the sake of causing trouble. Although it would be cool if you could get more invites based on your reputation on the site from people following you/upvoting you.