Apple's singular approach to handset design is extraordinarily encouraging to software developers. They know that one app will be compatible with millions of devices.
On Android, on the other hand, there is such a massive proliferation of versions, screen sizes and underlying technologies that enormous effort is required to take advantage of Android's huge user numbers.
5. Manufacturing efficiency.
Multiple models requires multiple factory re-toolings, multiple packaging sets, multiple user manuals, multiple everything. The end result is that iPhones tend to be more profitable than other phones, because once everything is set up, Apple's manufacturing partners just churn them out. Economies of scale lowers costs.
6. Designer focus.
Handset companies all have designer teams tasked with conjuring up new models. At the big Asian giants like Samsung, LG and HTC, the energies of these teams are scattered and fragmented across dozens of lines, and wildly varying approaches to creating great handsets.
At Apple, there is always only one next phone for all designers to focus on. That may contribute to Apple's superior design.
7. Consumer clarity.
And finally, it's a well-understood phenomenon that most consumers feel some degree of purchase paralysis when confronted by overwhelming choice. Should I get this one or that one? What if I get the wrong one? What if I buy the latest awesome Android phone, and a better one is announced next week?
Apple's single current iPhone model and fairly predictable upgrade cycle eliminates choice-induced purchase paralysis.
Whether Apple's approach -- or Apple's one phone -- is right for you individually is your own judgment to make. And, no, I don't expect Apple's competitors to suddenly achieve enlightenment and focus all energies on a single handset design.
But I also don't expect any company other than Apple to sell 600,000 handsets in a single day, sight-unseen.