They have - at Ford it's called "X-Plan." $200 under dealer invoice, and you get whatever incentives are available. My '07 F350 King Ranch, crewcab, dually 4x4, diesel, with the Tow Boss Package, power rear window, upfitter switches, etc. etc. --- $43,650 out the door including TTL. Sticker was right at $54K.
You should be able to buy any vehicle from an American car manufacturer for dealer invoice if not less. They have "holdback" on the vehicle which is a rebate from the manufacturer to the dealer equal to 5% of the MSRP. You can't get into their holdback, but you should be able to get them down to invoice or 1% above invoice.
GM has the equivalent of X-Plan. You just have to know what's available - it's called "smart shopping."