Fade, I have an interesting theory:
PPS is the affiliate betting the site retains poorly.
revshare is the affiliate betting the site retains well.
PPS is the program better thier site retains well.
revshare is the program not being able to afford to do PPS!
(last one is a bit of a joke). There are some programs I love revshare on, others where I know the pay per signup is just a better bottom line for me.