That's a good question. Going back, if I can find it in my notes here, the original premise was that cases funded by the program had to be of substantial importance, have legal merit, and affect more than one person. I suppose one could add to this that they need to be in some way setting a precedent because you can't hear every single possible case. Otherwise it would be a multi-billion-dollar program.
On December 6th, 2006. See this statement in context.