No negative terminal in power supply

I'm working on a project that relies on the Roomba vaccum cleaner's reference document (shown below), there are two positive terminals and 2 ground terminals. I'd like to understand:

1. Why there isn't a negative terminal, only positive and ground (this isn't a typo, I measured the +ve-ground terminals with a multimeter).
2. Why there are two positive and two grounds instead of just one each (couldn't a user easily break a single terminal into two if he needed to?).