Or is the overrepresentation of the late 60s and early 70s just an effect of expansion? Over-the-hill Original 6 goalies who would have retired otherwise hung around for quite some time after 1967, so maybe that is just skewing the numbers.
I'm thinking that's what it is. The number of inductees is pretty consistent all the way from 1924-2008, fluctuating within a nice flat range of 5-7 per season. The only exceptions are within the decade of 1966-1975, and there's even a nice little bell curve up to 11 in 1970 and then back down again.
If we look at those seasons in detail, I think we can chalk it up to:
1) The sudden influx of roster spots in an imbalanced league, which extended some careers (Sawchuk, Plante)
2) The popularization of the platoon system, which extended some careers of older goalies (Bower, Plante, Sawchuk, Worsley)
3) The advent of air travel combined with the long schedule, which necessitated true backup goalies even aside from the platoon system
4) The fact that guys like Hall, Plante and Bower were simply athletic freaks who played a lot longer than anyone could have expected.
Put all those together and you get a few years where there were about half a dozen stars of the previous generation who stuck around past their normal due dates.
It's kind of interesting to speculate whether this causes us to overrate the goalies of the Expansion Era, or whether it's actually causing us to overrate the goalies of the Original Six who picked up quite a few accolades under favorable conditions. Do we think of Plante, Hall or Worsley quite the same way if they get bumped out of the league by Parent in 1968? Or is it Parent who has to toil in the minors instead of developing into a legend in his own right? Food for thought, but I think it helps explain why the numbers look the way they do.