You could say that Apple is so far dominating the market for apps in portable devices. Or you could, like a Gartner report reported by Ars states, say that Apple is absolutely obliterating the rest of the field. Using their slide rules and impecable guessing abilities, they've concluded that Apple is responsible for all but .6% of the global market in app sales. And that is without a tablet store.
That's just the begining. As app sales increase, estimated revenues go from $4.2 billion in 2009 to $6.8 billion this year, to about $30 billion in 2013.