Here's my input to the "great debate"...
I admit that if I had a choice, an A-10 (or A-10-like) capability for a CAS mission would usually be my first choice in a survivable environment. However, that doesn't mean that it's an absolute requirement. I know I'm a bit dated, but out of my 250+ FAC missions in the OV-10 (Vietnam), 125 or more of them did CAS support at some point during the 3-4 hour sortie. I don't recall a single one of them resulting in the good guys being overrun due to poor CAS capability. Only one resulted in a friendly fire casualty and that was because the idiot stood up to get a picture of a Mk82 hitting the bad guys about 75 meters away (the ground CC's immediate comment was something like "Never mind, it'll save me the time it would take to beat his stupid ass to death").
The point of this is that we did great CAS work nearly every day with no A-10s. I worked F-100s, F-4s, A-4s, A-7s, A-1s, A-6s , VNAF A-37s, and F-5s, AC-119s, AC-130s, and even some AH-1Gs and UH-1Cs (gunship variants), plus my own pitiful ordnance, of course. Most of the work was in the 100-300 meter range, but some as close as 30 meters. In some cases, the sheer power of the 30mm may have been a detriment...the 7.62 was actually safer to use and plenty good enough in terms of killing power with less collateral damage potential.
Each platform had its good and bad points, and had to be used carefully to maximize impact on the bad guys and minimize threats to the friendlies. For instance, a light platform with small ordnance (like an A-37 with 7.62 and 250lb slicks) I generally started working close with guns and backed up about 10m a pass until it was safe to use the 250s. When I had a couple of A-6s (usually VMA 225 out of Danang...really good at CAS!) I'd put one or two mk82s as close as possible to slow the action, then start dropping sticks of five or six (remember, they has 28 bombs each) behind the bad guys about 300m then march the sticks forward about 25m a stick. It didn't take long for the bad guys to figure out they were soon to be caught between a wall of bombs and fire from the friendlies, and they backed out fast. It might have helped that the first sticks tended to take out upper management, watching from the rear, early in the game!
In general, F-100s were not too bad, since CAS and other close support was a large part of their mission, and the Marine A-4s and F-4s were very good at CAS since that was almost all they did (especially the A-4s from Chu Lai). They averaged between 20-40 CAS sorties a month and were very good because of their sortie rate. On the other hand, the AF F-4s from Danang (Gunfighters) were usually terrible, but that's because most of them only flew a real CAS sortie once or twice a month. I hated to use them closer than 200m. The VNAF guys were pretty good, too, but most of them had been flying for a decade, with the leads frequently having 1000-2000 combat sorties (mostly CAS) over a decade or more. Navy (mostly A-7s) was my last choice, mostly because they rarely did actual CAS, and I saw them infrequently which lowered my confidence in their abilities.
As a matter of fact, my feeling is that good CAS may be less about the airframe than the pilot experience in the cockpit (and maybe about the guy directing the situation (air or ground FAC, or whatever the current nomenclature is). The Marine F-4/AF F-4 comparison is a good example.
Just a thought...