Off topic again, but still worthy of discussion ....
I have several friends who spent many years selling vehicles at dealerships, and you're *somewhat* correct, but not completely.
What people often fail to realize is that the "0% financing for well qualified buyer" promotions are often handled by the auto manufacturer. The dealership offers it, but doesn't have to build the cost of the interest into the price you pay for the vehicle, because the manufacturer covers that for them.
(So that guy who posted about asking how much less you'd pay with a cashier's check vs. taking the financing may have actually found it would be the same price either way.)
Negotiating on price is starting to evolve into something only worthwhile on used car purchases. With new cars and trucks, the dealerships tend not to make a whole lot of money on the sales directly from you "paying too much". (Yes, some dealers purposely inflate the sticker price or "pad" it with relatively worthless extras like rust-proofing or pin-striping on the hood/doors. But you can figure that stuff out just by price comparing the same vehicle at multiple dealers in town, without so much as speaking to a salesperson first.)
Most of the time though, the dealerships make the majority of their profits from the in-house financing (including things like extended warranties that the financing guy tries to sell you as you're actually closing the deal), plus money received on the "back end" from the manufacturer for making the sale.
The Internet is the biggest factor for this change.... It's just too easy for someone to get educated about a new vehicle and what it SHOULD cost. And dealers with a good price can make a sale anywhere in the country, via sites like eBay Motors, vs. only having the "reach" of walk-in customers living nearby.
That's why you negotiate the price of the vehicle and then do financing. You should never purchase a car without knowing what you're paying for it. If you're just negotiating for a specific monthly payment, you're going to get screwed.