And who will be initiating and paying for these lawsuits?

Copyright lawsuits can only be initiated by the copyright holder -- the person who wrote the code being copied. StackOverflow does not claim copyright ownership of a user's comments.

Which is exactly how Wikipedia and others work.

Which is my (implicit) point. The userbase of SO does not include entities who have any incentive to litigate to protect their posted code.

New startup idea: acquire copyright to stack exchange solutions (there must be at least some authors willing to sell out), sue companies, patent troll style.