I think one vastly overlooked point is that GM is trying to slash it's sticker prices and increase other incentives to sell their cars. And it's becoming the only way they can actually move a vehicle off the lot - the lure of thousands off an already inflated stickerprice. And the cars they build which actually are close to sticker in value, however few there are (Corvette, GTO, Solstice) are kept in short supply. In the past, it's always been a common and, well, rather smart idea to lowball an offer for most any GM vehicle because the sticker was inflated. Long, arduous haggling was always more prevalent in any domestic dealer than an import dealer.

Conversely, Honda and Toyota need minimal if any incentive to move their product. People shopping those brands (myself included) go to the dealer knowing exactly what they want - model, trim level, color, options/accessories, and price. They have done extensive research, and pretty much have come to make an educated offer. One that ensures some savings off sticker, but isn't a lowball figure because they understand they won't get it for some massive discount. In other words, the car they are looking at sells itself, and they don't need to talk to a salesman about it