"Hmm, would you get the same slow-cooker tenderizing effect with a pressure cooker, I wonder?"
In a word, yes.
The tenderization effect comes from the break down of connective tissue, collagen, into gelatin. When that begins to happen, things start to get real tender real fast -- fork tender, in fact, where you can pull the meat apart with out having to cut it with a knife.
The true key to that isn't dry roasting, it's braising. Liquid in this case isn't a lubricant, it's a medium through which heat transfers far more effectively than air.
A slow cooker is a low heat source. You're lucky if you can get one up to more than 200 deg. F., even on high. I can BARELY get my slow cooker up to a boil along the edges, the center is usually 10-20 degrees cooler.
And, even if you do get it to the boil, you're only going to get it up to 212 or so deg.
A pressure cooker, on the other hand, raises the cooking temperature to around 250 deg. F. At that temperature collagen in the connective tissue starts to break down rather quickly and you can cook a pot roast a lot faster.
Grisly is also quite correct about chicken (or even beef) bones. Bones are held together mainly by collage. Dissolve that out, and the bones will get really soft and crumble.
I frequently make my own chicken stock. The old way was to cook it in a stock pot for upwards 8 hours to make sure that all of the collagen dissolved and you had lots of gelatin in the stock.
I've started using my pressure cooker to make stocks, though.
I can do in roughly half an hour with the pressure cooker what it takes all day with an open stock pot.
