I agree with that sentiment.
A SIM card that can be removed would allow you to both change your carrier after purchasing the phone AND perhaps change your phone and keep your carrier.
A removable SIM card is proven technology. They are going to a lot of trouble to create a non removable SIM card.
It's less about enabling customer choice and more about making sure that choice happens at an Apple Store.
They want the traffic that would otherwise go to a carrier store. If you go to a carrier store you might (gasp) accidentally buy something that's not an iPhone and be subject to "fragmentation". Plus the carrier would get a commission for the iPhone instead of Apple getting a commission for the service.