The sad thing is, I suspect Bethesda might think similarly. I agree most people would just be looking to get the DLC for free and I agree that forum participation is a good measure against that. It's just really discouraging to me when I've been reading all over these forums for months and I would totally report bugs, but because I'm kind of shy, I will likely not get selected. Still though, I'm holding out hope until I know I'm not in. Either way though, I think I'm gonna try to start contributing on this forum more often.
I am similar, i did not join the forums until recently as every time i would go to report a bug, numerous accounts of said bug had been reported, so i figured that there was no reason for me to join, let alone post, but with the beta it gave me a reason to join because i know i will be very active if i do get selected to join the beta as i wish to help Bethesda perfect their DLC so no one will complain about the bugs and turn away from the game as i know many people who did not enjoy Skyrim simply because of the bugs that plagued it early on.