That's too "on the nose"... too specific for me. I don't want to imply there is a cost associated with posting. More of a general measurement of the community - X comments last week, for example - that I can extrapolate to MY perceived usage. "Wow... I posted a LOT last week. I'm gonna give em $10." As opposed to, "it costs them $0.06 every time I post, so I'm not going to post this idea I had."
Data analytics are a cool and geeky itch that I assume a lot of us like to scratch. ("Information is Beautiful" anyone?)
By publishing some interesting stats like "comments over x period" or "posts during the Obama administration", it makes us feel more like a community, and inspires us to give back to that community. To support the tools we have been using to create this groovy Hubski group of people.
(PS - I do marketing for a living. So... yeah.)