There's a lot more to CAS than simply how many bullets your gun has. In any case, it's often not the preferred weapon. Bullets are indiscriminate. Small, precision warheads are becoming more in favor because the safety margin is better.

We've been seeing quite a bit in Afghanistan now where CAS is actually being performed by a B-1 carrying a SNIPER pod, sitting up at medium altitude with a large load of small precision bombs.

But that shows you the type of environment Afghanistan is, where the Air Force can deploy high value assets like a B-1 to perform CAS, because their anti-air threat is non-existent. The Air Force is not developing the F-35 to fight insurgents, they're deploying it to fight a well equipped, conventional force that will have multiple layers of sophisticated weapons. They'll do everything they can to soften these up before the strike aircraft go in. But there /will/ be some that remain, and its in this environment, that the F-35 needs to survive.

In the low-threat environment against insurgents, you can do that job just as well as the A-10 with the A-29 as the article states, for ever cheaper.

This is the conclusion that the Air Force has come to, and that's why they're retiring the A-10.