An example, if I have 10 browser windows open and one of them is playing audio, I would expect the specific window that is producing sound to have the "playing audio" icon on it, not the other 9 windows, as it is now. It's not likely a user wouldn't know which application is producing sound, however it would be far more likely they wouldn't know which window of an application is producing sound.
*** This bug has been marked as a duplicate of bug 375943 ***