I believe Dustin and his caddy were very aware of the local rule. They just didn't think it was a bunker. There are countless places on that course that become "sandy" lies after the gallery has trampled the course for practice and tourney rounds.
With the gallery crowding in (even standing in the same bunker while he hit) and no marshals willing to push them back it really was impossible to tell it was a bunker and not just some worn patch of ground. Yes the rules official won't offer advice unless asked but this is a ridiculous rule too. Think how much play would be slowed down there if every player asked for
a rules official on every shot from outside the fairway, which I would
certainly do on that course. With the wind blowing like it was there were countless shots taken from areas usually considered out of play. It would have been a 2 day final round.
So under the guise of officials not offering advice, then why did a rules official advise him not to
sign his card? If they were truly following their rule of don't offer advice unless asked, then they should have let Dustin sign the card and DQ him all together. Nobody told Roberto Divicenzo not to sign his improper card at the Masters. Same for DQ of Sergio Garcia at the PGA when Boo Weekly marked down the wrong score for him. Very inconsistent behavior by the so called officials if you ask me.
Up until this tournament, the bunkers at Whistling Straits that were "out of play" had always considered waste bunkers, therefore players could rightfully ground their clubs. I forget the player but some controversy at the last major there caused the PGA to make a very stupid decision by declaring every single bunker on the course on regular hazard. By doing that they should have also prevented ANY spectators from.
Rules are rules, and I'm all for them, but they should be applied consistently. This was horrible judgement on behalf of Pet Dye, the PGA, and the on course officials.
I also feel sorry for Martin Kaymer a bit because this whole mess has detracted from his outstanding accomplishment. I will say that I have a new favorite golfer (well top 3) named Dustin Johnson and I hope he comes out next year and smokes the field in every tourney he plays in.