iOS does not have an ENCRYPTED boot loader. Right now cracking one is tough. But you CAN install other things on it. This goes for all devices so far in all of history. It's only a matter of persistence. These new ones will never, ever allow you to install another OS. Not without the magic key.
You're right pragmatically; who gives a shit, less than 0.00001% of people run something besides iOS on their iPhone. That isn't the issue at all. The issue is that although their isn't a perceived choice, it still exists. Just because it's ignored by the majority doesn't mean it doesn't exist.
I mean, aren't people worried about this? Intel is trying to sell CPU's with DRM for unlocking cores basically; if hardware limitation gets paired with encrypted boot devices, overclocking could literally become illegal. At least under the DMCA and most likely ratified super-ACTA/CISPA.