We're all in Europe / Australia and the US disk supply is done differently to here (where the factory supply the countries which supply the dealers). Have a look at
NAVTEQ Maps and Traffic who make the US disks..
There are head unit updates for the US COMAND system (MCS-II) but I don't know if any are required for newer maps. There were a couple of map releases here in Europe that needed firmware upgrades to fully work (for instance for traffic management to work in France), but they basically worked without the upgrade, only new features werent available.
Cheers
Richard