>keylogging code on the SIM card or baseband processor

That won't work.

>Has Apple publicly claimed that they will also refuse to push individualized compromising code updates to devices on demand by gov't authorities?

No, and even though I strongly doubt the government would even try to do this and even more strongly doubt Apple would comply, their new tech (apple pay and touch ID use hardware support to even protect against this sort of breach which shows that they are certainly thinking about it). I'm pretty sure Apple won't even have the ability to silently push an OS update (if they did then someone could find out because it would be in the OS and then all hell would break loose) - it would have to be accepted by the target which means there is a reasonably large chance of detection.