Mark,
Maybe they sense a difference especially when you ask for it - but I think it's something the audience trust is a decision better left for the filmmaker to decide. They just want to be entertained. Think about your wife, girlfriend - your parents etc. Have you ever heard them say: Man, they should have shot the movie on film/Hd instead. (not talking about Dogme's shaky camera movements)
Of course you should opt for the medium that pleases you. But don't make the decision based on what the audience think. If it's entertaining - they'll eat it raw. That's my opinion.