Yes, because the systems for disengaging the wheels from the drive train won't work without power.

Is that a fail-safe or the opposite of a fail-safe? I can't decide...

Consider a battery failure while parked on a hill

Park usually does two things--it slips a fixed tooth (pawl) into a gear on the output shaft of the transmission, effectively locking the driven wheels (i.e. front wheels on a front wheel drive car.) It will also unload the gears of the transmission the same as the neutral setting. This is why on some AT cars, the idle speed will creep up a tiny bit after put in PARK or NEUTRAL.

Does it not have a "park" setting? How does "park" work in a car with an automatic transmission anyway?

Doesn't it have a handbrake?

Does it require more power than a tow vehicle can supply to provide that disengagement?