USB-C is the other piece of the puzzle. USB-C is really one cable to rule them all: the cables are reversible, and support all manner of communication and display technologies. It's also the only port on the new MacBook: you'll find a headphone jack on the opposite side.
Smaller components and the lack of any sort of fan leaves plenty of room inside the chassis -- for batteries. Apple's using a new battery design to cram as much juice as possible into the machine, so you can expect 9 to 10 hours of battery life.