I believe it fits the overall SONA suit better this way. As the design throughout the Winamp windows becomes a little more consistent. But as a personal preference, I liked the gray at the bottom. It sort of kept the buttons from flying out of bonds. And If you were to carry this design through, you would need to do the same to the Video-window, which would be enhanced if you could fit them 'tilted' buttons on it. Another way to approach the problem is to box the elapsed time and below controls in again.
Hehe, winamp sucks that way because there's so many limitations in skinning, especially when trying to match an existing visual style. And Im not pro at skinning like Blueslaad so its even harder. Thanks for the comment tho