but a back protector may save your spine and the elbow/shoulder armor may help prevent a break and disperse the impact into a more of a roll off/slide than "crunch". i've been a victim of a hit and run while riding my bicycle -- going 27mph and had to be helicoptered to ucla's er. also gone down on a motorized 2 wheeler a couple times (1 armored, 1 not). riding the bicycle, the helmet saved my skull and life, but the rest of me in skimpy cycling gear was severely beat up (knee, ribs fx, lots of stitches/road rash). let's just say i'm a believer good protection makes a big difference.
so at 50 mph, instead of nothing will really help, i think besides counting on luck, something's can potentially help and prevent catastrophe.
anyways, not intended to be a rant. just want folks to be safe and here's to none of us needing to test either theory. would break our hearts to hear about any gorgeous aero/lost world/langlitz/schott jacket getting torn up ;-)