The primary principle of HN isn't startups, it's interestingness. Ads don't tend to be interesting. Being money-related isn't the issue.

https://news.ycombinator.com/newsguidelines.html

https://news.ycombinator.com/hackernews.html

Apparently it is, given how fast free (gratis) alternatives always get posted regardless of how interesting it might be.

Well, the general upvoting of the free versions of things seem to indicate that it is pretty interesting to a lot of people here. I mean, not everyone here is in a position to pay for these things especially when in many cases you don't know what you are getting or you are not in a position to judge it's value.

Gratis stuff down the street is always more appealing than the $1 lemonade stand just in front of the door.

I believe that's a simplification. I think people tend to respond with alternatives--hopefully allowing discussion of comparisons. There's a bias towards free things because of barrier to entry and aversion to spending money. I see paid alternatives brought up often in discussions.

I would hope if a person is selling something there's a material improvement over free offerings--even if that's as minor as a unique voice, audience, or presentation. For example, the parent link is a series of static html pages with Javascript examples, while this post is a video series with compiled examples using SDL with extras like a discussion forum. I can see a good reason to pay money for that, but I can also see the appeal of the free alternative depending on your goals.