Read this thread: http://www.e90post.com/forums/showthread.php?t=772078
The 2013 map update on CIC iDrive systems (2009+) is via USB stick rather than the older method of loading the data from DVD. Pre-March 2010 cars which haven't had a system software upgrade can't read NAV update data from a USB stick. These cars apparently need to have their system software upgraded first, then the NAV update can be applied. I may be wrong about the date.
I'm guessing your dealer is pricing together the labor to do the car software upgrade plus the cost of the FSC code to activate the updated NAV data to your car.
Seems there's no way around the software update if it's not already been done for some other reason. Probably will cost you a couple hours dealer labor. There is a cheaper way to get the NAV map update and FSC code. Details in the referenced thread. In theory you should then be good for any future NAV map updates via USB without additional car software updates.