No, it isn't their job to ensure the viability of the small programs out there, but it is in their long-term best interest. A good analogy I heard the other day in a discussion on the NFL lockout and the salary cap. While it isn't the responsibility of the Giants or Cowboys to prop up the smaller market teams in the league, without the smaller market teams the league wouldn't be as profitable and thus the Giants and Cowboys wouldn't be as profitable.
In other words, the big school college hockey programs , regardless of how big, powerful, and profitable they become, will always need opponents to play. And if you start losing programs, at some point that will hurt college hockey to the point where even the big schools will see an effect.