Let me give some more reasons has to why Wolf, would not have been chosen as promotional DLC, one thing is Wolf is not guaranteed or confirmed 100% to return in Zero, and no you can't argue you can't have a Star Fox game without Wolf, cause the original didn't have him. Also you can say, well there's that's Star Wolf mode thing, but thing is games have content that doesn't always make it into the final cut, so Wolf may not return in Zero, sure we've confirmation that Pigma returns, but that doesn't mean all of Star Wolf will, cause Assault did Pigma is more then wiling to work on his own.
Another reason that Sakurai probably knew Miyamoto was going to delay to who knows when, and don't say Sakurai wouldn't know if Miyamoto would delay it, need I remind you they've worked together for a long time, Sakurai probably knows Miyamoto and his Game Design habits very well. And seing as ho Sakurai wouldn't know when Zero would be delayed and no guarantee that Wolf would return he really couldn't be used to promote Zero.