Growing iPhone Development into a Viable Business (~$100/day with ads)
seoxys.com
seoxys.com
But yeah, there is no magic like having already written code. All additional work you do (marketing, new versions, SEO, etc) acts as a force multiplier for all the work you've already done. It's capitalism at its finest (since you're leveraging intellectual capital).
Plus you can always play the "Hey, if I can write one application and make $100 a day, and the application doesn't take the majority of my time to maintain or support... couldn't I write two applications and make $200 a day?" game.
How well does a coffee shop scale? Not so well. Space in the real world, is not free. Space on the internet is essentially free.
You also seem to have assumed that a graph that has grown from 0 to 100 in 2 months, is now going to stop growing and stay at 100 for a year.
Off topic: Love the about: "mobile is the future" in your profile.