I wouldn't say that the ALNM nomination was obvious (I live in LA and am out here infrequently, when I do, usually I gravitate towards seeing plays, but I did see ALNM, Fela and American Idiot [AI in Berkeley]), but if I were a nominator, I probably would have included it, but would have ceded something to American Idiot as well (which had, in addition to the amplification aspects, some interesting content choices throughout the show).
As far as a win, my money is on Kaplowitz's work in Fela, which has a rather effective wrap around quality to it (much like elements of the scenic and lighting design).
And, returning to the original thread topic, yes, the Enron design was the one nominated design which truly added impact to the show, rather than sound effects called for in the script or only transitional music (all of which is important, but design can [and should be at times] so much more).
The one show everyone on Broadway is waiting to see: Twyla Tharp presents: Big Bottom - The Spinal Tap Jukebox musical!