Before StackOverflow existed sites like ExpertExchange. They are irrelevant now despite the fact that they had tons of content whereas StackOverflow started with 0. People ask questions and answer on StackOverflow not because that's where the most content is, but because that's where most people are. I think license is just a manifestation of the company's philosophy, and personally I don't think I would care much even if StackOverflow changed their license tomorrow BUT kept their philosophy and policy in tact. (Which they should, since they know better than to alienate their users and they've seen what happened to all the sites that alienated their users)