For the Apple store in particular I've seen it get so crowded without adequate app discovery mechanisms in place that it seems like without serious marketing money you're essentially rolling the dice on how successful your app is going to be. I don't really want to spend a bunch of my time on that, when I could spend it on other pursuits.
But maybe this is a mistaken perception? Why do you think it's so simple to do? Just because you've found success or is your approach different than the norm somehow?