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.