Depends how long you've been listening to podcasts. There are lots of shows I listened to regularly for 3-5 years that I've completely stopped listening to because of the sheer volume of advertising (plus the fact that every week/day/episode the advertising is exactly the same). All TWiT Network shows for example are unsubscribed for me despite listening to about 10 of them and not missing an episode for years. So, in some older shows, saturation has definitely been reached. I think a lot of it is to do with necessary spending.

Podcasts are so simple to make yet people put together networks that have these high-end studios and camera systems when all they really needed was some guests, a few $100 mics and Skype.