Nice job raging against the GP because your OS doesn't have a feature that's standard among pretty much every other modern operating system.
To respond to the second part of your post, no, it would not be inconvenient; it would be *ideal* to remove volume control from each application and have it controlled by the OS.
The key would be to not have it buried 10 layers down. While it's not quite ideal (imo) in every operating system, there is already a volume control widget in most operating systems. This widget can be expanded to list the applications accessing audio, and I can adjust their volumes the same way I adjust the volume for the entire computer. Even in Windows Vista, it's already in there, and is pretty easy to get to, and in Ubuntu at least, it's fairly simple as well.