> but that market isn't big enough, IMO, to sustain the growth that Apple, Samsung, etc have enjoyed thus far.

Which is why Apple is pushing so hard into "Developing markets" like China, Brazil, India, etc. etc.

There are hundreds of millions of people on the planet that have never really even had the option of buying an iPhone or iPad. I'll wager tons of them have the means to buy one, and they clearly have the desire.