I think it also has to do with reducing resonations when the AFM kicks in.... I used to hear the valve cycle when it would transfer back and fourth from V8 to V4 mode. Anyone who has changed out the exhaust (cat back) has removed these valves.
2011 Silver Ice Metallic 1SS/RS+ Convertible. Completed modifications so far: installed factory HUD, deleted AFM/DOD, Dynatech LT coated headers with high flow cats, Solo Cat back exhaust, CAI inc. intake, Vmax ported TB, SIM quarter flares/splash guards, steering wheel radio controls, PDIM iPod interface in center console, RX catch can, JRE cold air scoop, windshield washer bottle relocation.