I think the reason people cheer for the heels is because they act as heels and are proud of it. I love the heels more in the current state of the WWE because of this. You have so many faces out there like Carlito or Cena, who really act like heels but want to be cheered and loved and seen as faces.
This is all the result of Austin and the anti-hero era that was the Attitude Era. The crowd may just be desperately waiting for another "say your prayers, eat your vitamins" face and I think that may be very close at hand with CM Punk. It is so refreshing to see a true face in the business.