SAT Shot - Proves Missile Defense or Not?

According to a briefing by Vice Chairman, Joint Chiefs of Staff Gen. James Cartwright, the recent successful shoot down of the wayward spy satellite was not a test of the missile defense system. While the Missile Defense Agency was helpful in netting all the sensors needed together, according to Cartwright,

the missile itself is a standard missile in the Navy inventory; the ship is a standard ship in the Navy inventory. We added a lot of instrumentation. We made some modifications to the software to be able to go after a satellite.

You know, this is a one-time mod. It is -- if you put this mod in, we can't use the ship or the missile for another function without taking the mods out. So it's not something that we would be entering into the service in some standard way.

Yet, Defense Secretary Robert M. Gates said the shot proves that missile defense works.

I think, actually, the question of whether this capability works has been settled. The question is: Against what kind of a threat (do we employ the technology)? How large a threat? How sophisticated a threat?

So, is this shot "proof" of missile defense, or just a one-off highly constrained, albeit successful, experiment?