Yeah, I think YC applicants or founders is statically insignificant, but I think your total user base is just as insignificant as this since it doesn't tell us much about what stories are showing up on the front-page and who is saying what about it. Instead, considering you're still only interested in comments, what if you filtered your user base for anyone that has posted a comment in the last 30 days then extrapolated the proportion of comments posted given a threshold of karma or "days alive" on HN against everyone else in your user base.

I think it's more revealing this way if you are interested in how increased traffic and site participation is effecting this 6% you mentioned above or that "days alive" value; IOW, how is increased traffic and new user participation effecting the rate at which this sample is posting comments?

In the end, I don't think increased traffic is effecting the discussion to the extent that it really matters; I think what really keeps everyone else in check is the frequency at which older members are posting comments.