The best part about FireWire (from the perspective of someone who never actually used it) was that it was very tolerant of uneven voltages; thus, all iPods that could use it (which went at least through the first Nanos) had very, very inexpensive car power adapters - they could just use the "12V" that's really more like 13.4 V. No real circuitry inside, just a cord to plug into the iPod.