I think we have an apples-to-oranges comparison here. Yes, we can currently access LiveATC for free by computer (which helps generate ad revenue for the site), but using the iPhone app is not only NOT a revenue generator, but it's also a major luxury and convenience, as are most things on the iPhone. (At least, on my iPhone.)
Then add to that the fact that developers like Dave spend countless hours and sleepless nights writing code, debugging, testing, and then going through Apple's approval process before the app even hits the store. Philosophically, I think $3 is a bargain both for the app, and for saying thanks to a developer for giving me something additional to listen to in the car, or wherever I want.
Now, having said all of the above, I'm personally struggling with spending $99/year on the WingX app, even though it's cheaper than buying a Garmin Aera 410 outright. I will break down eventually and do it.