I am not so sure blades were really better then. OK there were the Personna 74's and some long lasting Wilkinsons but those blades were not cheap, so the cost per shave wouldn't be less. I usually get more passes from less sharp blades and less passes with the sharper ones but that is, as Crixus pointed out, simply physics.
There might also be another explanation, apart from "everything used to be better in the old days", for the life span differences as far as they really excist. I mean, I often take 3-pass shaves with the last one being a ATG-pass. There is no real need; my shave is socially acceptable after 2 passes but I just feel I can do better and go ATG. But it is excactly that ATG pass that needs a sharper blade to be comfortable so when it starts pulling there I toss it while it is still ok for one or more WTG/XTG passes.
So I do not just get less shaves because of the extra pass per shave but also because I throw it out sooner. I bet without the ATG I can get 6 or 7 shaves out of blades that give me 3 now.
I must to the barber's, monsieur, for methinks I am marvellous hairy about the face