Since the app still runs for those who already downloaded it he's not really turning down $50k/day from the in-app ads. He's just turning down the potential incremental income that would accrue from additional downloads.
This.
If he was selling it, he would be turning down cash. He isn't, so he will keep making for as long as people keep playing it. Which, arguably, he has vastly prolonged by making the game the forbidden fruit. Maybe this isn't a stunt, maybe he is one smart guy with a perfectly reasonable strategy of maximizing profit while minimizing his time and labor.
P.S. Maybe I'm a fluke, (and definitely not a gamer) but this is the first game I've played since Planets vs. Zombies and Angry Birds (not counting Wurdl, which I have played all along). The fact that he hooked a non-gamer like me really shows something -- maybe just dumb luck, but maybe he is way smarter than he is being given credit.