I don't see it as nasty, just an observation of various facts that lead me to believe (perhaps incorrectly) that the post has ulterior motives. But since you ask, this is what lead me to comment how I did.

- HN is about sharing and opinions, so I decide to share mine.

- The poster opened an HN account 4 days ago and the startup was launched 5 days ago.

- "Open Letter" titled posts almost always leads to someone bashing a product or individual. Imagine how relieved HN will be when they see that it is indeed a "heart warming" thank you letter...did you feel good reading this?

- Without the product the startup wouldn't be here. All credit goes to Balsamiq while conveniently encouraging you to view the startup.

- And, as a software developer (who has one more than once been NOT paid for services rendered) this one really raises my suspicion. The poster received the software 8 monts ago and will get the $79 to Balsamic ASAP.

Anyway, right or wrong, that is how I came to my original comment. I'll take my down votes if necessary.

edit: formatting