As far as the power goes, a non-sub port is probably necessary. Based on my experience with my S7, charging via usb would only lead to complaints.

I believe in the battery testing thread, it is mentioned that typical wires in a usb cable are good for about 1amp of power. At least for me this seems to be the case. Using a modified typical usb cord to charge, the charging rate seemed to be about 1/2 of what the stock 2amp charger (even with a charger providing 2amp). Using a heavier duty cord, it charges at a rate close to that of the stock charger.

Charging at around 1amp will very slowly charge the battery when in the car using the tablet to navigate. In my mind if you used usb charging, many people would grab any old cord to use (as a spare to keep in the car, at work, etc). The tablet would charge slowly, and you'd end up with a lot of complaints.