There are four excellent ways I can see to make money on the app store.
First is to get hired to write an app. That market is burgeoning, for the simple reason that iOS is the first priority platform for brands that want a presence in your palm. Typical customers don't want to hire and manage an app developer, they want a full end-to-end service. Prices have been high, and the market is growing, so there's every chance that there's room for another player if you're great at sales and willing to work hard.
Second is to create a brilliant app and spend enough money to get it the eyeballs it will need. No-one has a perfect record, so you should be planning to push a number of apps out there to be reasonably sure of success. And you need to do the numbers carefully, because you're spending money ahead of making it, and while you can always arrange to spend more cash, you can't always just turn up the revenue tap. Bear in mind that some of your competitors are already spending amounts on promotion that are only justifiable on customer lifetime value, not on the purchase price, ad network income or freemium conversions.
Third is to push apps out fast and keep cranking the handle. Individual apps will make modest amounts of money, and whenever you find an app that does a little better, produce variations - the same idea targeting a different interest, or geography, or demographic etc. The lifetime income graph has a fairly well established shape, and this pattern supports a lot of solo developers and small teams.
Fourth is to get lucky. From time to time, somebody's getting lucky, and it may be you. The odds are better than a lottery ticket, and if you're working to make compelling user experiences then you're sitting on the tree lightning strikes most often. You and rather a lot of others.