Spotify does, however, sometimes lose their license to songs on the service. Maybe not often, but it's happened to me enough that I only rely on Spotify for discovery now -- when I know I like something enough to keep listening to it, I buy it.
I agree with this recommendation. When we are dealing with a company as large as and has as diverse a portfolio as Google, we must be heedful that as soon as they find one of their products troublesome in one way or another, they will shut it down. With a company like Spotify, they will fight for its survival as if their life depends on it.
With Google, it seems to be, "This was a fun experiment. We'll try something else now."
For music, I think the best option is to find indie labels who let you download and keep stuff DRM-free. Spotify is probably the best option for mainstream music.