Mid course gates have been used to keep the action centered (VOR in-port races have used them). Probably not needed for the AC because of all of the digital wizardry.
Leftovers from the start box was really my first guess, but I couldn't recall whether the start was in the middle of the course, or above the windward mark (it's been mid-course for most of the ACWS). Even if those marks have propulsion for self-positioning, getting them off the course fast enough is probably more of a risk than leaving them in place.
As an aside, I listened to a lot of the Murray press conference, there's a lot there that tells me he's a stand-up guy.
