WP8 Storage question

I want to get a Nokia 820.
However it only has 8 GB internal storage.
While it does have expandable memory, i need to know how WP8 manages its storage.

What I know is that apps must be installed to the internal storage.
What makes me uncertian is whether an app can store its data to an SD card.

I'm thinking mainly of a Spotify type service. I mainly use online streaming for music, with offline playlists.
8gb is even less than my current HTC titan, which is stuffed, mostly by spotify AFAIK.

I was hoping WP enabled offline data like this to be stored in the more spacious sd card?
Anything else you can tell me about it's storage managment would be appreciated.