Yes. Like most successful internet applications, Serverfault and Stackoverflow are middle-men. They provide a forum where people can ask and answer questions. The value of a 'middle-man' or brokerage application is a function that is upper-bounded by the square of the number of punters. This square law is very nicely documented in an essay called 'Content is not king'
Thus, the more questions (of reasonable quality) and answers the more people get value from the forum and the more valuable the forum is. Joel and Jeff both had a base of readers that they could refer to the site - this is why they could get Stackoverflow off the ground where most people couldn't.
Thus, the more (decent) questions the more punters are attracted to the site and the more content the site has access to. The upper bound of the value is proportional to (number of good questions and answers * number of punters). The more the merrier.