It's not really possible for them to put the time up there. If you think about it, when you're just scrolling on the home screens, it's not taking up much battery so it'll show a certain amount of time. But then when you're playing a graphics-intensive game, the time will be dramatically less. In turn, the "time" will seem inaccurate, especially to a user who doesn't understand why the battery gets drained faster in certain situations.