I don't know. I think it runs the other way around. With a very supple tire you can run a lower pressure, as the increased flexing of the sidewalls will not convert as much rolling energy into heat. With the stiffer tire you don't want the sidewalls flexing so you max out the pressure to limit this. As stiff as they are, the sidewalls of a Marathon are still quite flexy under the average cyclists weight. I'm pretty sure that's how it works. At least it did until Rene Herse (who makes supple tires btw) convinced everyone to use high(er) volume tires at low(er) pressures which made everyone want to do the same, whether they were working with the right kind of tire for that kind of treatment or not.