Blown coverage is most often the result of good offensive scheming. They don't know who we're going to throw it to, so it causes problems for the defense.
I don't think our team really views us as having a #2, #3 or #4 receiver. I think Crayton, Hurd, Ogletree and Austin are all capable of filling that role. Crayton has the upper hand because he has been here for a while and has had success with Romo. But I'm of the opinion that we have a crop of guys who can all step in if needed.
One thing I've always said about Romo is he is one of the best at spreading the ball around and reading the field. Blown coverage is what a QB is supposed to look for. If everyone is covered, then there would be no play on offense... just food for thought.