The thing is, if you delete all the posts, you can say goodbye to CF's PageRank. From a business perspective, PR is the most important thing. Getting new members to view ads...I doubt David will want to lose that. All the guides and such that have been posted on here in the past 4 years just disappearing would be a killer.
On the other hand, I know if some members lost their precious post count and rep, they would be very unhappy, and possibly leave.