I can understand how you see it as advertising but in my case it's not. I've needed a plugin like this for several projects and couldn't find anything like it so, as a learning exercise, I decided to build it. The plugin started out as a basic free version I submitted to wordpress.org and after I saw how many people downloaded it I realized it could potentionally be something useful for a few people. I decided to add more features and out of curiosity I threw it up on code canyon just to see what would happen.

Making this post on hacker news was also for curiosity's sake. I've never released anything and was curious what the hacker news reaction would be. So far, zero people have bought my plugin but I've had a lot more encouragement and well wishes than I imagined I would get. In my opinion, the encouragement and support is worth a lot more than making a small amount of money :)