I've wondered about this for a while. I was reminded of it this morning when I found I had left my car keys on in the "accessory" position overnight, resulting in a call to my local auto club.
If you read the instructions for using jumper cables (read the instructions? BWAHAHAHA
) you'll find that you are supposed to attach the black clamp from the cables onto some grounded part of the car's frame, NOT to the negative terminal of the battery. Why is this recommended? And if it's so important, how come nobody ever does it?