Before the Gulf War, any missle or rocket fired had a 100 percent chance of NOT getting shot down. Why? Because the technology didn't exist.
Now, there IS a chance of shooting down a missle or rocket. Who cares what the percentage is, every one that is shot down means less casualties and should be celebrated.
This is like complaining that every bullet out of a machine gun don't kill something.
I would assume hitting a missle with another missle is no easy task. The shrear fact that it CAN happen some of the time is freaking amazing.
Heck, for the skeptics that believe they don't work at all consider this.... AT LEAST THEY ARE TRYING! :P