Scenarios:

1) I have an odd sound in my Volvo and go to a qualified shop where I describe it to the best of my ability
2) Same odd sound, but I go to a Volvo enthusiast website and ask others for their ideas

Responses:
1) The shop mechanic listens to me and my problem and suggests ideas for a solution -- he/she never says "there was someone in here last year with the same problem -- call them and ask how I solved it".
2) The Volvo enthusiast board generates a variety of responses, most of which are useful and helpful but some of which say "this problem has already been answered"

Why?

P.S. This phenomenom is repeated across the web on a variety of enthusiast websites which might focus on anything from consumer electronics to cameras to frozen pizza!