I would say that has to assume Apple doesn't pull any game-changing tricks, which is not likely to be correct knowing Apple. There was the iPod in 2001, the iTunes Store in 2003, the Intel switch in 2005, the iPhone in 2007, and the iPad in 2010. Another's due before 2014. It probably also assumes Apple sticking to a single carrier past 2012, which is not likely.
Of course what Apple could do to increase market share is just make more iPhones. iPhone 4 supplies are still constrained months after the release.
“I would say that has to assume Apple doesn’t pull any game-changing tricks, which is not likely to be correct knowing Apple. “
Thats a fair assumption. I’d also expect their competitors to make changes as well.