This is assuming an asymmetric multiprocessing model. It may be that the hardware is set up as such, but symmetric multiprocessing is also an option which is what the Pi seems to do.
No, this works fine for symmetric configs. The OS can treat all the CPUs the same once they've booted, you just need to pick one of them arbitrarily to run the initial bootup code, which is conventionally the one with ID 0. Calling that one 'primary' and the others 'secondaries' is just convenient terminology when dealing with this kind of bootup code.
This is how the Pi is brought regardless of if you use SMP or AMP.