I guess for a community that talks about how much they love cars, it works better.
Have you seen the bloodthirsty animals that plague the forum? Ever hear the mantra, "Jaywalkers deserve death," echoed by much of the anti-zebra coalition?
Unlike the analog universe, where you can simply choose to exit a conversation with a dedicated idiot or shill, would you not have to choose between sorting through enormous bloat (without fees) or extreme new/unknown-user segregation? A concession for newbies is multiplied by several magnitudes for malicious spammers. The value-based filters will target both bloat and unrecognized users: if you want to see or merit new-user activity, you will need to tackle an ungodly amount of spam, effectively becoming a voluntary moderator (but only for what sections you deem important).
It's an interesting premise but isn't the capacity of spam too high?