Don't really think a provider "should" offer anything other than what they post as their rate. That said, I'm sure regulars are more likely to be more regular at a lower cost or higher return (more time).
Not sure about newbies, tho'... That might send the wrong message - personally. "So I get to see you once at X, then it jumps to Y unless I see you how many times then it drops to..." That could get to be a hassle. "Newbie friendly" is probably the best offer a guy can get just starting out.
My opinion - take it for what it's worth. I think I fall into a "grandfather" situation but have yet to knowingly take advantage of the "offer", so I may be waaaaay off base with what I think about "most" and "many".