There is one centralised bottleneck - Apple's iTunes podcast index / search API - which seemingly everyone else in the company has forgotten about and runs pretty openly for anyone to submit to and use.
There are also a handful of essentially CDNs that host the .mp3 files themselves, but these are more or less completely interchangable. They're just infrastructure for hosting files.
I'm a very (very, as in: too) avid podcast listener and the fact that apple run one of the biggest "phone books" has literally never stopped me from doing anything podcast related. I find new podcasts just fine, by word of mouth as well as in other directories.
The only player in town that seems to really make a dent in the openness is Spotify which have been aggressively buying out podcast teams and taking them off the open web, and that's one of the prime reasons I cancelled my subscriptions.
Then there's smaller losses like the BBC4 which made most of their podcasts have a 1 month delay vis-a-vis their own app. I have no interest in that. In effect, this just served to curb some of my compulsive newsy consumption. If something isn't important enough to still be heard a month later, maybe I didn't need to hear it in the first place.
Anyhow, I very much agree with the article and I'm happy someone made the point so much more eloquently than I've managed in my many debates about the matter.
There are also a handful of essentially CDNs that host the .mp3 files themselves, but these are more or less completely interchangable. They're just infrastructure for hosting files.