I think it depends of is the SW1 and SW2 shortcircuited or not, not on the cartridge case itself
It has some metal brace near the middle of cartridge slot hole so cartridge is pushing a switch when you insert cartridge, and if there's no cartridge when you push on it - computer turns the power off. we used those with YIS-503IIR at school instead of reset button because reset button is at back side and inserting finger to slot was more handy 
i suppose the whole circuit works together with signals SW1 and SW2 on cartridge to turn power on when cart is completely inserted and visa versa. i have the front small pcb from 805 with two slots on it (bought cheap by occasion) though when i go to Kiev i can take pictures so you can check if that's true, because i only had a brief look. i personally prefer to turn off computer still, because it may become dangerous habit incompatible with other computers ;) f.e. Wavy 70FD don't have any protection...
