Here's the thing that people are missing out on when discussing the "War for 64"...
Say ND decides to join a conference and picks the ACC. UConn follows. ACC has 16.
Pac-12 takes the four we expect them to take. Pac-16 is created.
ACC and Pac-16 successfully lobby for two automatic BCS invites per conference.
SEC invites KU/MU/KSU as 14-16.
Here is what the Big Ten has left to pick.

If you are competing with the same three or four entities for TV dollars, wouldn't you want to do whatever you can to ensure one of those entities has the least attractive options? If you're Mike Slive, and you don't have the academic restrictions that Jim Delany does, would you want to be aggressive and potentially shoot down one of your biggest competitors?
Most of all, if the ACC has the eastern seaboard locked down, do you want to further entrench your dominance into the southern states with schools like Louisville or USF, or do you extend your stretch into the Heartland, where there are much more ardent football fans and keep three rivals together and bundle them with an SEC school that's never had one?
Mike Slive and Jim Swafford can destroy the long term viability of the Big Ten with five schools. If you take Kansas, Kansas State, Missouri, Notre Dame, and UConn off of the table, the Big Ten's options are almost nil to get to sixteen. ISU and Rutgers are good academic fits. After that....