Apple already offers two iPhones. They just don't call the better one the 'pro.'
The "pro" is the current year's model. The "non-pro" is last year's model at a discount.
I know that's not what you meant, but that's their answer to your question. This arrangement works out well for them I can't imagine them changing it.
For starters, you're asking them to make the BEST iPhone the one with the smaller market. The current system makes the best phone the most popular. Under your system you basically get: "Hey, all you people buying iPhones...most of you don't have the best one! Ha ha, suck it!"
This works with laptops and desktop machines because people realize that professionals need (and will pay for) more powerful computers than you need at home. That makes sense. "Yeah, I know there's a $4,000 Mac Pro out there, but this iMac is just fine for me, thank you!"
But mobile phones are different. People won't like the idea of buying a second-rate cell phone just because they can't afford a $1,200 phone. The existence of such a phone actually makes the regular $700 iPhone look worse because now it's no longer the best iPhone out there.
Steve loves to get up and say that the iPhone is the best phone on the market. (Never mind if there's some other phone that's better, he can ignore that easily enough.) But with an iPhone Pro, he couldn't say that anymore. He'd be robbed of his best pitch for the phone that 90% of his customers are going to buy. It would make a lot of people shop elsewhere. "Well, I certainly can't afford the best iPhone, so maybe I should buy the best Android phone..."
That's the textbook defintion of shooting yourself in the foot.
