On a long enough time scale, iOS could be relegated to a smallish percentage of the market, roughly equal to OSX in the PC market. Apple's self-imposed limits are attractive to a certain subset of people, who really like the Apple way of doing things.
We are already seeing that Tim Cook will not allow that to happen, and is diluting the laser focus of Apple's products to appeal to a larger subset of people. Apple is building two different sizes of iPad now, and the rumor mill is discussing at least two different iPhone models as well.
In the end, Apple will find themselves either limit themselves to that small market, or else the die-hards will complain that Apple has "lost it's soul" as it expands into different directions as they attempt to appeal to an ever larger user-base.