If, indeed, three teams are leaving, presumably Caterham, Lotus and Sauber, then Ecclestone would be forced to introduce three-car teams.
His contract states he has to provide a grid of 16. While mathematicians amongst you may note that 8x2 is, indeed, 16, that would mean that should one car fail to start, Ecclestone would be in breach of contract. Which means that if one team fell out with him, their withdrawal would cause him to lose money. Too much of a risk!
This contractual clause is why there were 14 Michelin shod runners bothering to take the formation lap at Indianapolis in 2005.
I think there has been a lead up to this. Think, for example, about the car numbers situation moving from the team-based system to a driver-based system.
In addition, the Vettel/Webber situation showed Ecclestone that two drivers only in a team could lead to some very dull racing if the best car was only driven by one driver capable of doing so at that stage of his career. And with 9 top 5 seats to go around, there is likely to be more opportunity for the likes of Nico Hulkenburg to actually reach the top drives, rather than Warwicking his career to its conclusion.
To provide a counterpoint, there are advantages and disadvantages to this. Although we could see all-silver podiums quite frequently (although only one 1/2 since Austria suggests otherwise), we would have a three-way fight for race wins rather than two. It sees more talented drivers less blocked from the top seats, but more risks in driver choice as well!