So we can guess tiefling have a devilish ancestry, rather than a demoniac one.
I always thought the two category (demons and devils) did not make sense at all, because it was mostly impossible to guess if a particular creature was one or the other. So, I think this is a move in the good direction.
However, I felt a disturbance in the force, as if millions of Planescape's fan suddenly cried in horror...
Btw, erinyes are somewhat more interesting than succubus,
IMHO. I guess the sword wielding furry born of the blood of a god is more interesting than the average whore-demon. And the name is cooler, too.