I would say it's a bit like Windows and Mac OS. Some would prefer control and openness over usability (Windows, Android users), others wouldn't (Apple users).

I agree with Pierre, just want to mention the economic fact: Iphone ( just as all Mac devices) are more expansive then anything else,  and  the gain in usability does not always worth the price to pay.

iPhone is a pretty expensive device.
But Apple addicts are everywhere, I am not one of them...

What we are facing now is just a trend effect, people get iPhone because if you have not, you are a geek or a 'has been'...

People don't buy iPhone because it's the best terminal ever, but much more because it's a nice device and workable without spending much time on it.

Simplicity versus Functionality

I would like to clarify something about point 1

iPhone is a product name and it doesn't mean that it is 1 device (maybe one casing, but in anyway it's the same device) 

Currently there are 3 different Models (even if most of people call them iPhone)

- iPhone

- iPhone 3G

- iPhone 3GS

Same with sales figures when an analysts say "iPhone has been sold at 26 millions units" I would say that it's like saying "Nokia phones have been sold at 250 millions units" is this sounds the same? no

Same mistake was made about Motorola RAZR (100+ millions units with V3/V3i/V3r/V3x/V3pink/etc...) or LG Chocolate (Millions units but with different models)

You are a bit playing with words mohamed ;)
But you're right, so to correct my point one, iPhone only runs on 3 different terminal but all from Apple.

Which is not the case when speaking about Android which be run on a lot of devices, and so updates are far more difficult to maintain.