Yup. This helps power the "instant" playback that I'm sure the author has enjoyed. Saving money on bandwidth, I'm sure, also helps them pay for all of the licensing agreements they have with the recording industry so that you can stream that impressively large catalog for free.
(ii) Spotify has a right to allow the Spotify Software Application and the Spotify Service to utilize the processor, bandwidth and storage hardware on your computer or other relevant device for the limited purpose of facilitating the communication and transmission of content and other data or features to you and other users of the Spotify Software Application and the Spotify Service, and to facilitate the operation of the network on which the Spotify Software Application and the Spotify Service runs.
Granted, it's not listed as a "feature" but you agreed to the possibility of it.
Does the author expect the service to stay free and also remove the p2p features that make it work? Okay, yeah, sort of because he wants to be able to limit bandwidth. But not really. Rather than complaining about upstream traffic, he complains that Spotify should make the non-monetary costs clear upfront.
This is the point of the post - there is a cost to "free" as we all know, and here is one good example. There's nothing wrong if a service is p2p, it should just tell you. Barring that, users of any "free" service ought to keep in mind that it might cost them in other ways.
You're paying for other features... let's say the cost of Spotify not being P2P increases the price by N dollars per month. The "free" users pay N, paying customers pay $5+N or $10+N. I think it's different to complain that they don't offer a "non-discounted" payment plan to opt out of P2P.
It's actually a hybrid. The most frequently played songs are on Spotify's caching servers, and the first ~15s of those songs are streamed from them. The rest of the song is streamed via P2P, as are the entirety of the less frequently played ones. I seem to recall also that Spotify will locally cache songs you play frequently as well.