Isn't it the case with almost every subscription service that there are aspects of it that you don't make use of? I feel like every subscription I have, from cellular to cable to Netflix, there's stuff I don't use that is part of the subscription. E.g., I don't watch horror movies, but apparently Netflix is still making them. Maybe I should take issue with it, but it just feels so mundane to me.
You're talking about genres, which is a different scenario.
This is more like Netflix raising prices for streaming subscribers to fund a new video-game studio. The fact that some people might enjoy both doesn't make them anything like the same thing.
I think it's just levels of granularity. Podcasts and music are both audio entertainment. It's like Netflix adding TV shows to their lineup of movies.
But the broader point is simply that in subscriptions to services you usually pay for some aspect of the service that you don't use and never have any intent to use -- and you can partition off that aspect of the service in a simple way (at least simple to you).
Car rentals and horseback rides are both transportation, but most people would say the difference is not trivial.
Movies, tv, and video games are all visual entertainment, but video games are different enough that most people are generally not happy about the idea of raising the price of Netflix to finance a video game studio. Art museums are visual entertainment as well, but raising the price of Netflix to build art galleries in select locations wouldn't fly well, either.
In this case, Spotify is doing anything but partitioning off podcasts. As many comments here reveal, most people are seeing podcasts pushed heavily in their music interface.
