(Yes voltage spec for a USB port is 5V. The most common USB port (USB2)
can supply up to 500mA per port)
USB port powering and charging is very common, and most phones seem to use it, as well as various and sundry gadgets like reading lamps, mini fan, dashboard hula dancer...
Actually, single port cigarette-lighter plug type USB power ports are very cheap... and they should be, you can buy the few components required to turn 12v to a well-regulated 5v supply for under a dollar. The hardest thing to get ahold of in the retail parts chain is USB sockets, though that's improving too.
As long as you have at least one 12 vdc lighter installed close to the nav station, you'll be able to use those USB or auto-charger adapters.
No doubt he can put his finger on the problem.
(Never ever thought I'd get to use that smiley... another thing crossed off the bucket list)