IMO after 10.5 hrs of cooking those ribs shouldn't have been fall off the bone, they should have been bone fall out. I wonder if you didn't have more than low temp issues if you kept them in an oven for 4hrs at 250 and they still were not tender. Pops6927 talked about braising in his post and I think he brings up a very good point. Foiling ribs is a braising technique, the liquid in the foil packet gets hot and steams the meat to tenderize it. In your rib experiment it looked as if the ribs were bathing in the apple juice. With so much juice in the pan I doubt that very much steam would be created unless you kicked the temp up significantly.
If you take the next 3 lb rack that you buy and cook it for 2hrs @240F, then make a foil boat(using heavy duty aluminum foil about a 12" longer than the ribs), place the ribs in the foil with a 1/4 cup of apple juice, seal it tightly, put it back in the heat for 2 more hours and when you open the foil you will see the steam escape from the inside and that means tender ribs.
I also think that you might have better results if you raise your cooking temp slightly, say the 235-245 range, that's just an observation based on my own experience.
Good Luck on your next rack.