I guess I'm a prime example of your point. My rate is $400/hr and I offer a $20 discount for P411 users. Here's my reality:
1) I don't want to see more clients. My rate is higher than average because I like my comfort zone of only one or two per day that I work (which is nowhere near every day) and I'm still making a very comfortable living, with a ridiculous amount of freedom.
2) P411 screening saves ME nothing. I have an assistant. I pay her the same amount whether she has to do newbie screening, or P411/reference screening. There is no incentive for me in offering a discount. The $20/off I offer is simply a courtesy for the guys that like to "pay" for their P411 accounts with the discounts they can get through them.
3) This is the ONLY public discount I offer. I never run specials. I never discount my rate. No, $20 doesn't matter to me or the vast majority of my clients either way. If he's THAT worried about a discount, I'm probably not the lady for him anyway. And I'm fine with that. I'm pretty sure my gents are, too. They don't want me to discount. They want me to be too expensive for many to see, because they want me to be fresh-faced and eager to see them on any given date, not tired/stressed/sore/pissy. So, high rates means I'm always at my best to see them. Other ladies do it differently. This is just the way I do it.
4) If I remember right, the only reason I started offering a discount on P411 in the first place is I think there was some sort of incentive at one time, if not now. Whatever that incentive was (if I'm remembering correctly), it must have convinced me and I've just kept it there, because 90% of my clientele ignores it anyway.
I hope that might have cleared up some questions for you. If not, at least now you understand my "hooker logic."