That's for the ads on adwords and yahoo.
So, if I get 300 extra page views/day just because more content is free, that's the equivalent of $30 advertising or $900/month.
So, to compensate for that "loss in traffic" if I was restricting access to these pages, I would have to make an extra $900 from sales.
If the access everything membership was strongly enforced, right now, I might make 2-5 extra access everything sales/month.
Checking this out is just a game, I know...
Still, it is another way of looking at it...