All it takes for you to fry something is to bridge the connection from a rail carrying power to a non powered portion of the board. This is anything that is between the mosfet or transistor acting as this “hardware interlock” as you call it. There has to be a live rail somewhere on the board when the battery is connected else there would be no signal for the power button to let through so the unit would actually turn back on. Hell, even if this interlock was somehow right at the connection where the battery meets the board and power went absolutely nowhere else (including to the power button meaning you couldnt turn it back on) all it would take is for you to drop something conductive on the exposed positive pin of the battery and for that to make a bridge to a neighboring circuit which even if that doesent cause damage you could bridge further down the road. Why take the chance?

You also have capacitors that hold a charge after powering the unit off its not much power stored but it’s certainly enough to blow a component. The correct procedure is to unplug the battery and press the power button after the battery is unplugged to discharge any latent charge in any caps