I saw a clip of them playing acoustically recently and they were absolutely mullering a Rare Earth tune with all their might. Which is the kind of thing musicians who are still fans will do out of the best possible motives. A bit like Springsteen and Costello failing to find the inner groove of London Calling but blazing through it anyway. I like that Metallica seem to care about mainstream rock still meaning something if only as a vague rallying point for the terminally pissed off.