As they went about answering their own question, seems like WikiAnswers was able to offer a little insight:
Why are question and answer sites so popular? Someone actually asked that question on WikiAnswers. The answer given suggested it was human nature. “Some people like to share with others what they know. Some people like to learn by reading the questions and answers.”
Here’s the original Q&A: Why do people like question-and-answer sites?
What can you add?