like I implied but not necessarily required nation wide.

Take this one consideration of a time slot...2-3pm CT start times tomorrow...

http://lsufootball.net/tvschedule.htm
http://www.big12sports.com/fls/10410/tv_radio/FSN_Color_National_Map.pdf?DB_OEM_ID=10410

You'll see the 8 games below listed as one of these FSN affiliated stations.

Florida State at Duke 2:00 p.m. FSN Affiliates (HD) / ESPN-GP *2 / espn3
Colorado at Washington 2:30 p.m. (RSNW / RSRM) (HD)
South Florida at Connecticut 2:30 p.m. (SNY / MASN) (HD) / ESPN-GP / ERTV / espn3
UCF at SMU 2:30 p.m. FSN (HD)
UMass at Delaware 2:30 p.m. CSNE / TCN (cable)
UTEP at Tulane 2:30 p.m. DirecTV - 623 / FCSC (cable)
Western Michigan at Northern Illinois 2:30 p.m. CSNC / ESPN-GP *2 / espn3 / Live Video
BYU at Oregon State 3:00 p.m. DirecTV - 617 / (FCSP / KBYU) (cable)

FSU/Duke and UCF/SMU do split the majority of the affiliate's in some what of a split national audience.

http://lsufootball.net/misc/fsnaffiliates.htm

But that still leaves 6 other games being played that dip into the national audience. Note that two of those games not on the majority of affiliates feature 2 BCS teams (CO/WA and S FL/UConn) and then another features BYU/Oregon St.

Just one example demonstrating how I understood how the FSN's work. Now pick a time slot where it is one of the only games slotted for FSN and I agree that the regional's "need" available content and will use it.