Yep. It's almost like Apple knew if they hit it out of the park (which they did) by 3GS/4 time it wouldn't MATTER if other manufacturers "caught up".
There will always be "spec whores" that will jump ship when Samsung tosses in a "Deci-Core" processor (that still somehow manages to lag through the latest Android release for some reason...), but by and large, by capturing the mass market as early as they did, Apple has cemented the majority of it's user base.
Carriers know this. They know people HAVE to have an iPhone. People line up to pay MSRP for iPhones. People went to AT&T (a loathed service) just BECAUSE of the iPhone back when it was exclusive.
So now they advertise that they have it, and they do "xyz" better, or give you more of whatever, or charge less, etc...
Because the MAJORITY of people don't give a flying crap about other phones anymore.
Apple won. I have mixed feelings about it (I admit I used to love when the iPhone was "cool" and edgy, and now even grandma has one...), but it's pretty obvious that no one else even comes close with a single model.
Carriers are just smart about it, nothing wrong with that.