If everyone did this (for cases where it actually mattered. Some app types are supported fine by in app ads) I would love to see how it would change the entire market perception towards paying for software. Right now it's viewed as a risk. A "should I make my app a paid for app or not?". I'd love to live in the utopia of developers simply being able to look at their creation, say that this is the value for it, and have people respect that.