A pertinent point is raised in this Wired article on the new iOS device sizes that are apparently coming later this year. In countries like the US and the UK, where the use of multiple devices is typical, the availability of a larger iPhone or smaller iPad is arguably not a game-changer but simply a "small part of the mix".
But in other countries where the mobile phone may be more of a primary device for users, the availability of the phablet form factor may more strongly influence users' choice of platform. For Apple to have such devices as part of its mix may then open up new markets for developers. As I highlighted in a previous post, the option in Xcode to test our apps on arbitrary screen sizes should probably not be overlooked in the coming weeks...!