I checked the specs on their webpage:
http://www.microchip.com/1010/pline/...8520/index.htm
it has FLASH for program memory, and EEPROM space for program variables. that means your program can store information as its running, that will be there next time you powerup - so you could save things like your yaw rate sensor zero reading, or any other variables you need to fine tune your control algorythms.
the 7.2 'backup' battery is probabally what powers the controller (most likely regulated down to 5V or 3.3). Lke someone else said, this is probabally so the controller doesnt reset if your motors draw a large current spike. We will have to see how it all works together.
BTW, the EDU kit last year, everything ran off a 7.2V battery.