You're exactly right. AF pilot here, not a Marine, but it is my understanding that all Marine officers go infantry school first. The Marines are very good at Combined Arms - it's what they do.
But that doesn't mean they are necessarily more committed to CAS. CAS is pretty much all A-10 pilots do. They live and breath supporting dudes on the ground. Objective #1 for just about every CAS training mission is something along the lines of "Achieve the Ground Commander's intent."
One key difference is that Marine pilot mostly provide CAS for other Marines. AF CAS pilots mostly provide CAS for the Army -- a completely separate service.
So going back to Objective #1, a Marine pilot could very well personally know that ground commander. Went to various schools together, crossed paths, etc. The USMC isn't terribly big, all things considered.
An Air Force pilot has about a 0.1% change of knowing who that Army ground commander is. Question becomes, does this matter?
A Marine may say it does, and I won't argue with him. I will say this, as a A-10 pilot: I don't give a shit you who are. If you need CAS, I will give you everything I've got. Even if all you need is for me to stare at building with my targeting pod for three hours to to see if any bad dudes are hiding inside. That's how I was raised, and that's what teach brand new A-10 pilots.
This is the background of the movie "The Blue Max".
DOD has a zillion ways they support the families of KIA soldiers. Even just looking at economics, losing 10 soldiers isn't cheap.
It's cheaper than losing the plane, the pilot, the resources spent in training, maintenance, and preparation of the whole logistic structure.
Not to mention the asset and its capabilities. After all, a grunt with a gun is less of a threat than a plane carrying an entire arsenal.
Someone cooked up a model showing that the embraer super tucano would have been more effective in the CAS mission in afghanistan than some of the high power jets we used, in addition to 10x cheaper.
I would love to see such airframes flown, they would be much more effective in many roles than "super-airframes" like the F-35. But that's not the US military philosophy. We fly the best and most expensive, even if it's 10x as expensive as an airframe that's 75% as effective. It's a calculation that government debt is cheaper than having to face the public over killed and captured soldiers.
Also have heard that ground commanders hate the high-altitude planes for CAS because they're less likely to correctly discriminate the situtation on the ground before unloading.
To your point -- yes, we don't operate AC208; I think iraq is the only one who does. (And if the sight of a hellfire stapled to the wing of a small turbopro doesn't make you want to run and hide, I don't know what will). But we also don't operate the F-35 in the CAS mission. neither plane is a good example of a CAS plane.
Even considering that hypothetical scenario, there's also the cost of training everyone throughout the logistics chain and required to get the plane operational and in the air.
If you lose a peasant, you lose a peasant. If you lose a knight, you also lose the squire, the page, etc etc etc.
The squire can help some new guy with his helmet, etc (I think this is considerably more true for modern military than for knights...).
I honestly don't know much about marine aviator culture, but I'd be very surprised if they don't see themselves as having more in common with marine infantry than air force pilots do. That commonality probably makes them a lot more committed to keeping ground forces safe when flying CAS missions. I could be wrong. I am speculating here. I'd welcome the opinion of somebody in a position to know better.