It's perhaps more important for the key to lock the steering than simply to serve as an ignition switch. You could hot-wire the ignition and drive off. That's why they started locking the steering column in the first place. And that probably means the lock has to physically be part of that mechanism.
All of which just means that designers ought to make sure you can see and easily reach the spot on the column where the key goes, without it being blocked by the wheel (airbag and all).