Though that was from a beta and in an unsure time of how the service would turn out.
Just because a service starts by doing dubious things, does not mean it will continue doing so.
They replaced everything in phases, because I remember all the URI:s to songs kept breaking in my playlists before they implemented auto-matching of your songs to new location once a specific album was rendered unavailable.
No affiliation to Spotify, just a long time user.