If this is true, then he (Craig Newmark) really needs to read the innovator's dilemma (http://www.amazon.com/The-Innovators-Dilemma-Revolutionary-B...). TLDR: If you allow yourself to become a prisoner to your success, you're actually making your continued success unlikely. You can solve the dilemma by spinning out a smaller, irreverant version of yourself & giving them what they need to destroy the old company.

In craigslist's case, he could include a link on the old site that allows users to upgrade to a more modern version, and have the modern site basically consume an api/scrape the old CL till it gained momentum.