Is it just me, or has the median age for post-postmodern rock stars been getting younger? How else to justify all those fawning profiles of suburban scofflaws Sum 41 making out like they invented disorderly conduct? Sure, it all comes down to what the marketing execs call "positioning," like how the Sums' video for the hooliganistic "Still Waiting" carves into the Strokes/Hives/Vines, while their concurrent spoofs of mid-'80s metallic bombast seem lost on the band members themselves, let alone their desired audience. If "rock" is indeed "back," who can tell the difference between the mooks and the mockers? Part of...