It's easy to attribute much of the continued success of the iPhone to the runaway sales the App Store has brought Apple. It's been so successful that numerous other vendors (such as Google and RIM) have modified their own sales tactics to at least somewhat match, if not mimic, how the App Store works. Despite controversy and criticisms over just about everything you could imagine, Apple has definitely crafted a potent marketing tool that continues to set the example for others.
Will they keep this success up for much longer, or will the next biggest competitor (Google) be able to overtake them? We also can't count out RIM, who has a big reputation and a lot of cash behind them. If Apple can make such waves in just a year's time, perhaps Google and RIM have the capacity to do such as well.