That is probably true for podcasts on exclusive platforms like Spotify, but those are few and far between. Even with those, I don't think Spotify is delivering customized audio files to each user.

It's more like with broadcast TV, where they have general demographic information that they use to attract advertisers.

The general case is a plain ol' RSS feed accessed by any arbitrary client. There's not much data to be tracked there. And there's not a whole lot you can do with an IP address without introducing highly-visible problems. You can infer the general geographic location of your listeners, but that's about it. If you try to do personal tracking via IP address, it's going to be messy. Cell phones don't typically have persistent unique IPs, and even most laptop users are going to be running on a shared external IP (e.g. at a college campus, business, or any ISP that does not provide users with a dedicated IP). And again, they're not customizing audio files per user. It's a mostly static medium.