Apple can ensure it's position in the mobile market for years to come by keeping updates regular, performance snappy, and the interface fresh. The latest upgrade to iOS7 reflected an overhaul of the UI, without introducing too much new functionality. Still Apple fans will be glad to see a fresh look, giving them the little incentive they needed to stick with their beloved Apple products.
People become invested in their mobile ecosystem, for most people it takes a big reason to switch from iOS to Android or vise versa. So long as Apple keeps pace with apps and functionality, there will never be a mass exodus. In this regard iOS7 was a smart move, the design UI doesn't do anything drastic but updates the look of the operating system to keep in touch with the times.
Apple products have always excelled in quality, and the latest OS upgrade is no different. Time will tell if that is enough for Apple to keep competing with Google for the #1 mobile mantle. For the first time since the debut of the original iPhone, Apple is on the wrong side of market share trends, it will be interesting to see how Apple develops further with iOS7 to regain the top spot.