The Big Ten (which is really the Big 11), and the Pac 10 are looking to add schools to give them some more leverage in new TV deals, to add big TV markets to their viewership area, and for the Big Ten to get to an even number of teams to split the Conference into two divisions and add a very lucrative season ending Conference Championship game. In the end this has everything to do with money, more than it does anything else.
Both of these conferences have their own TV networks, and they are looking to get the biggest audience possible for these TV channels. Since the Pac 10 already has two teams in LA (the biggest American TV market), the search isn’t as critical as the one the Big Ten is in. They are looking to get some of the New York TV market, and get some traction for a Bowl game to be held in new Yankee Stadium, set to feature teams from the Big Ten.
In a business sense the Big Ten is looking at Pitt, Syracuse, or some other Big East team to come over, and give their Conference a piece of the East Coast market. Since it looks like they will add more then one team and possible become the Big 14 or 16 Missouri has also been linked to talks of Big Ten Expansion. It seems that the Pac Ten has set their sites on Utah, which could be a move to pacify Senator Orrin Hatch from launching a federal investigation into the legality of the College BCS Championship system.