Conventional incandescent bulbs are not polarity specific. Current can go through them either direction. What the engineers did in the case is ensure this socket isn't chassis grounded through the console and is recognized to be different from all others. The console wouldn't be a proper ground path anyway.
I definitely get that. The socket is grounded back at the cowl. I understand that current can flow in either direction. I just don't get why the socket is not wired conventionally. (power applied to the bulb tip)