Well, it depends on age of the podcast really, plus the rate that they release new episodes.

There are lots of good podcasts that only release monthly, but of course that means just 12 episodes a year.

I don't know for certain, but I would imagine a weekly release is the most common rate of release. So even for a very successful podcast, if they're only a year old, they'll only have 52 episodes at most.

I guess what I'm saying is that quantity doesn't necessarily correlate to quality. And unless you're very successful and profitable, you probably can't release a high rate (more often than weekly) of episodes and maintain technical quality. Most podcasts are edited and published by the hosts, whereas super successful ones can afford to pay professional editors to edit and release however many eps each week.