Then you're paying for your user account with the cloud services, not the client apps (which you may not even use, e.g. if there is a Web version or a third party client).
Note that it's not really a Spotify streaming app, rather it uses your (free) Spotify account for playlists, search, recommendations, etc. and then goes and find the song you want to play on YouTube, and the lyrics from scraping websites I think. Pretty clever.
Then you're paying for your user account with the cloud services, not the client apps (which you may not even use, e.g. if there is a Web version or a third party client).
A subtle distinction, I know, but it matters.