very interesting. i have nothing to say, but would like to be updated on these posts.
as far as the Prius goes, if on a steep enough slope, the car will roll in the opposite direction of travel. have had it happen MANY times on some of the downtown hills of Seattle and that would be primarily in the drive mode.
now the power expended by creep mode is interesting and it would seem like there should be a locking mechanism in place that would prevent rollback in either direction and it could easily be mechanical actuated electronically when shifting.