I love the minimal look and the thought that went into the design. I will definite check it out further. It will be interesting how you fit the volume control into the component which at the moment looks really well balanced and laid out. (ie. How you might improve the already-excellent UI by adding something to it)
Some of us want background noise.
Think of turning up your system or browser volume for a quiet song, and then viewing a loud flash video. You might hurt your ears or disturb someone. Adjusting only your music player for songs without ruining your volume setting for some other source gives you a finer control.
Every media player on every web page could set its volume permanently to 100% and I really would never even notice.