Looks like the usual unsolvable "but the platform must protect users from badly written apps !!" nonsense, that just needlessly limits available application functionality.

Two examples which would this stupid decision make impossible:

• track logging in modRana, while modRana is in background
• batch tile download in background

Note that both is explicitly started by the user and the user of course expects that the application will continue working on the task until he again tells the application to stop. Not that the the system just indiscriminately stops the app once it is unfocused.