"What off the shelf centerfire semi-autos, regardless of type of trigger action or frame material do you find that are able to meet that accuracy spec?"
I don't remember stating that this accuracy spec. had to be met from the factory, but I'm told there are makers out there that can do it. Way out of my league though, price-wise.
I do own an old springfield 1911 wadgun that has a good BarSto barrel and tight bushing that will do it though. Even have an inexpensive RIA GI with a tight $30 bushing that comes very close. My M9, not even close; at least not yet.
"I read a lot of reviews, including ones of very expensive, metal-framed handguns fired from machine rests, and offhand, I don't recall reading about any off-the-shelf centerfire semi-autos that meet that spec. What I'm getting at is that if you have a pistol that will shoot 10 shots into 2" at 50 yards then it's safe to say that it didn't shoot like that out of the box and also that the things that make it so accurate have little to do with the frame material."
I'm told that the AMU struggled for years trying to get the Berreta M9 to shoot as accurate as their 1911's, and those frame were alloy. A friend of mine shoots with them and I've seen their solution. A big part of it was to add steel rails back into those alloy frames.
"Which means that if you're going to denigrate plastic framed pistols for not being able to hold 2" ten shot groups at 50 yards, that same negativity applies to any off-the-shelf pistol, regardless of frame material. "
You're right on there. That would be true for anyone still shooting bullseye today, which is why 1911 gunsmiths are held in high regard. I'm not denegrating polymer guns, they have their place. I just doubt it will ever be in bullseye though.