Actually, now that I think about it I have an alternate theory.
There's a very good chance I'm off base here, but on my Nexus 10 I've noticed that there are some very occasional graphical glitches ( back lights flickering, and horizontal lines) that have to do with things been overlaid on top of each other. Maybe the transparency was causing similar graphical glitches. That said, if that is the reason they decided to leave it out then Google really screwed up here. They need to fix the underlying problem, not just remove transparency from the status bar.
[sent from my nexus 10]