WP8 in contradiction to WP7.5 does not frezee applications that work in the background, which means they eat a lot more juice than they would on older wp.
Sorry I completely misread your comment. I thought you were saying all apps in WP8 aren't suspended in memory when you press the start button but keep running. I didn't realise you were talking about apps that were allowed to run in the background like skype or Nokia Drive. My apologies.Could you specify what exactly is wrong?
I got my info form here: source