That's a good point! My friend Ward Duncan, maintenance chief of the 9th PRS, said that the exploding turbo problem came from the early airplanes that used a lower gear ratio for the mechanical supercharger, making the turbo work harder. They upped the gear ratio in the later ones to give the turbos a rest, so they may have dispensed with the turbo armor. Aside from that, pilots were told to make sure the turbos were both spun up before takeoff, and the armor screens might make direct observation of the wheels rather difficult.
I have a Minicraft 1/48 scale P-38J that is in Yippee markings. I have not opened it yet, but I wonder if the 274-N radios are depicted correctly?