I would figure everyone here has at least once been sliding backwards down an icy hill and had to slap the tranny into drive and floor it. I have, and it saved my butt. I don't see where the opposite is any different. I say if you're running a tire size and combination that is large enough to break your drivetrain with just spinning your tires, then you're running on a thin line and its time to upgrade anyway. I agree with AxleIke and would much rather replace drivetrain parts than body work too.
I don't get the Ebrake thing at all. Seems like that would cause the rear end to try to pass you up on a downhill, much like having your proportioning valve adjusted too tight on the street.
Those who are saying to give it gas on a steep icy hill have obviously never been careening down an icy hill... the LAST thing you want is more speed. I was on a run and saw a Tacoma lock the brakes down a hill and pick up a significant amount of speed right into a pine tree... which proceeded to fold the ARB bumper over the hood, effectively sealing it shut so we couldn't get the fan out of the radiator. Dead rig. I came down nice and slow with my tire chains.
-'88 pickup - Daily driver, AAL's, 285's, ARB bumper, Warn winch, all around cool rig.
-'01 cherokee - 6" Long arm'd, 285's, ARB bumper, custom roof rack, electric locked D30, auto locked 8.8, trussed-plated-fortified.
-'12 Jeep JK - 2" lift, Skid Row skidplates, OR fab bumper