I don't want to say it from a position of superiority or anything, just different mobile culture, but in here, changing SIM cards is normal. It's what you do when you buy a new phone, because - as I said below - you get a SIM card separately, even when you buy it right with the operator with the contract.
But I guess it's a different culture
I've had 5 mobile phones...some candybar in the early 00's, a flip phone in the mid 00's, and iphone 3g, 4s, and now 6. I've never even /seen/ a sim card in person. It's a piece of tech that I shouldn't have to every even know exists. I just want my phone to work. I shouldn't have to play around with a microscopic piece of plastic and metal for that to happen.
I see it the opposite way. Every phone should have a part in it that is removable and replaceable and ensures that you can do whatever you want with your device. I was staggered when I found out that some US CDMA devices are literally unusable without the permission of the company you originally had service with.
If you want to buy a new phone and keep your number.... what do you do?
Well I guess you can just ask in the store to move it to the new one, that's true. It's just... strange.
You're letting yourself be constrained by the very brokenness people are saying should be fixed.