IMO the 50G avg for relievers is a tad high.
While long-relievers and set-up guys frequently appear in more than 50 games per season, guys like that don't put up the "glamour numbers" that are going to garner votes (wins, saves, strikeouts). A good case in point would be Mr. McEnroe posted above. Very impressive ERA and OAV, but people immediately scoff at the idea of him being in the Hall because he didn't put up the wins or saves.
The relief role that most people are going to deem Hall-worthy would be that of closer. And while LR and SU frequently appear in 50+ games, I think that would be on the high end of the scale for closers, since most people limit their use to a strict set of circumstances (leading by 3 or less in the 9th). They rarely come in at all during losses and blowouts. As an example, my longtime closer in Clemente will be an automatic nomination because he made 7 AS teams and won 3 FoY awards. However, if one of those seasons had gone south and he ended up with 6 AS and 2 FoY, he'd be on the outside looking in because he only averaged 49 games per season, and that seemed right on the average with the other closers of his day.
So, long story short, I'd be all in favor of lowering the 50G average for relievers, as patrick stated earlier can be easily done.