The only reasonable reason that I can think of for the NDA is to stem some of the "OMG THESE RULES ARE TEH SUCK!!!!!" that are going to come. There may be some game mechanics they want to hammer out before the public and the "haters" get their hands on them.
Yes, but by having unreliable leaks (and likely incomplete) they could very well be doing that, but in a way that won't let them respond.
In other words, they have set it up so they can't really comment on leaked NDA stuff, without losing credibility, but if it were open then they could - and it would be expected of them.
So no, still trying to see what angle they're trying for except for PR - and that's a risk I wouldn't take.