Oh yeah totally right, but there comes a time where no matter what you do, you're going to keep making less and less money out of the game because even though there are 250k new users ever day, the people that where interested in buying your app have already done so, and now only the passerby's and window-shoppers of the iOS world are looking at your app.
The cool thing is that now that you've been the developer of Trainyard, when you do reach a point where you should be releasing a new game, you have gotten so much credibility it isn't even funny. And off course that translate to more immediate sales at the beginning and a big chunk of extra steady clash flow at the end.