Apple's much-anticipated live-stream event later today has all the drama we've come to expect from the Silicon Valley powerhouse: A potential raft of new gizmos, showing off Apple's insistence on always one-upping itself. But behind the scenes, a much more complicated drama is playing out for the tech behemoth: Namely, Apple is running out of markets for its most successful product, the iPhone. The company's flagship device has already saturated the markets in the U.S and Europe — and it seems well on its way to saturating the market in China, too.