First, when zoomed out, outliers in all possible tasks become more common — internet commenting is just a subset for silly folks like me.
Secondly, the emergent human social fabric is built to recognize and amplify outspoken and / or talented outliers, via mechanisms whereby others who {agree, can find utility, can profit} are incentivized to act as amplifiers. The cost function to repeat a message drops precipitously every time it’s repeated (influences status quo). I’m not sure it’s particularly surprising that internet social forums behave by the same rules — and are even optimized to replicate them mechanistically (upvotes).
I mean... not be dismissive, I guess it does strike me as particularly neat that the internet provides a medium for these people to productively share insight and identify new niches where they can potentially add value to the rest of the world. Where would we on HN be without, say, patio11? :)
It's pointless to comment if one cannot add new information, perspectives, arguments, or humors to the thread, as a result, one really needs to make an effort to engage in the discussion. In practice, it means you'll need a proper keyboard, and a fast Internet connection to search for references. At least, at there, or at Reddit, or even at 4chan, this principle applies. I mean, you can make pointless comments, but you'll lower the SNR of the entire community, or your comment will be ignored or filtered on 4chan, or downvoted (or not getting votes) on HN/Reddit/Slashdot.
There are other places where the barrier-of-entry is lower, like the comments section below the stories on "ordinary" news websites (not HN), etc, but make an comment is even more pointless.
I guess the best counterexample I can think of is Twitter. It's no more than 140 chars and highly personal, so making a knee-jerk comment is common, and you can use a mobile phone instead of a proper computer to do so.