Hmm, that is true. There is no real way to close an app except manually. I was playing angry birds, yes I am new to the game and it's awesome, and don't like it sitting paused on my dock. I know it's just idle, but there needs to be a way to tell it no, end task as requested without going through the manual process.
Pandora is in the same box. Get it?
it's not in idle (angry birds), it's not anything. The state gets saved, and the app is closed. It is the same as creating a Game Freeze in a MAME emulator. You create the freeze, quit the game and emulator, come back to it later, and it restores from the freeze state.
as far as Pandora, the only time it is "streaming" is when it is downloading the audio file to play. I have an FM Transmitter in my car and notice when a new song comes up in Pandora, I hear the GSM noise in my speakers for a little while, but about 1/4th of the way thru the song (I am on Edge), I stop hearing it, which tells me that the song is downloaded much like an MP3. It will only start downloading the next song WHEN the next song comes up, and not before (because your choice of thumbs up or down could change the next song as well).
and as for apps that support background "local notifications", I would assume that these are done much the same as CRON jobs on any other UNIX machine, where a text file contains an instruction that should fire at a specific time.