App stores are just are likely to turn to crap. I've had lots of friends complain that they bought an app, and then an "upgrade" shoved advertisements in.
It's not third-party ads, it's first-party ads, which is slightly better.
Like OP, I have a lot of sympathy for software developers trying to sell in a world full of people who don't think they should pay any dollars for software. They are still gonna pay, just in terms of their privacy and computer security.