I suspect (but am no expert) that the main arguments for integrated batteries are actually to extend the lifetime and sturdiness; drop your Nokia and there's a chance the battery pops out and gets damaged, drop it in the water and the battery compartiment is a point of ingress.

I'm arguing that the sealed / glued / tightly packed / irreplaceable battery thing helps keep phones working for longer.

Of course the counterpoint is that often the battery is the first component to go, and this law is intended to make it easier to keep them in working order for longer.