Roger what you're saying makes sense in theory, but there are alot of exceptions to the don't give away too much rule.

A free site is supposed to be free samples to sell the sponsor correct?
So how do you sell a cumshot site or a gangbang site or an anal sex site with only softcore pictures?

What good does it do you to censor the pink on a big tits page? The surfer at that page wants to see big tits, which by the "censor the pink" theory are ok to show to the surfer, so he saw what he wanted to see and doesn't need to join a site now.

Why do movie galleries convert better than picture galleries? (Almost anyone who's ever done both will tell you that the movie galleries get more signups)
I'm giving away free hardcore movies and I get more signups than if I give away free softcore pics.

My theory on why retention is low has nothing to do with free porn, its always been out there and will always be out there.
The problem with retention is too many paysites. A surfer used to join Kara's or Cybererotica and stay for six months because there were no other options.
Now there is a smorgasboard of paysites producing their own content. You can buy 5 trials a month for a year and never see the same content twice.

McDonald's had better "retention" before burker king, wendy's, rally's etc. came onto the scene.