I think the main reason is because lipos come with bullet sockets, so bullet connectors plug right in. That makes them neat, simple and minimiszies the need for extra connectors. I much prefer bullet connectors to deans connectors or Tamiya connectors.

4mm connectors have been used for decades on things like power supplies, multimeters, audio equipment. I'm not sure of the resistance numbers, but they have worked fine for me. There are a range of high quality connectors available too.

To me it seems like the main disadvantage is that it is possible to plug them in backwards (reverse polarity). I've just adjusted the wiring on the ESC so that the positive lead is only long enough to reach the positive terminal on the battery.