I'm not so sure SO will lead to a smaller pie. The walled nature of EE limited its appeal to the largest part of the audience (the people looking for answers).

I'm not so sure SO will lead to a smaller pie. The walled nature of EE limited its appeal to the largest part of the audience (the people looking for answers). So although their business model was more direct, they were basing it on a smaller corpus, with fewer viewers. An indirect (advertising-based) model over a much larger number of eyeballs could well make for a larger pie. The challenge for SO is to see if they can maintain a high quality corpus as they scale, so people will keep producing and consuming their answers.