iOS 5. The upcoming release of the Apple mobile platform--iOS 5--introduces a variety of compelling features. Granted, many of the features introduced in iOS 5 already exist with rival platforms like Android, but the new functionality may attract users to the iPhone 5.
iCloud. Despite perception to the contrary, many iPad owners don't also own an iPhone. iCloud could change that. The automatic and seamless integration between iOS devices and a Mac or PC make a compelling case for using iOS on both the tablet and the smartphone.
There are a wide variety of awesome Android phones, so I don't think Android as a whole needs to be concerned. However, Apple is already the number one smartphone manufacturer in the United States, and if demand meets expectations that gap could grow larger. On a platform level, iOS will probably still lag Android, but on a device level the iPhone 5 may annihilate the competition.