Edit:-it's all a carry over from road racing,there's a lot of it about
I just checked and my Large size Audax bike has a 74 degree seat post and is a perfect fit with an inline seat post despite my long legs. I use KERS but still creep forward on the saddle. I ride decent distances and just returned from the Pyrenees by the way - so endurance is top of my list
The forum is full of threads from people who can't get their saddle far enough back,especially those who ride Brooks saddles.
Spa's frame designer and one who's opinion I trust implicitly and who designs slacker angled seatube is of the same opinion,check his designs out for a chap who knows his stuff.
As I posted up thread you could get the saddle in the same position with seatube angle 2degrees slacker than your present frame and the bike would none the worse for it.