I think it's the general texture of the "LOL", smiley emoticon, and exclamation more than the gratitude. A comment that doesn't add much, and looks like it was made quickly often produces bad results here.
Maybe it's because people are scared of losing the fantastic signal:noise ratio that's a hallmark of Hacker News and is very hard to find in internet discussion. The parent comment looked like more general internet discussion, but if he'd written, "This is exactly what I needed to hear in plain English: I keep meaning to code up this simple timezone app but I've been scared to execute it. Wow, that was valuable" - well, that probably would've been quite high in the positives.
Maybe it's because people are scared of losing the fantastic signal:noise ratio that's a hallmark of Hacker News and is very hard to find in internet discussion. The parent comment looked like more general internet discussion, but if he'd written, "This is exactly what I needed to hear in plain English: I keep meaning to code up this simple timezone app but I've been scared to execute it. Wow, that was valuable" - well, that probably would've been quite high in the positives.