Dealers and manufacturers have reacted to the wide availability of invoice pricing. Invoice is not the real price the dealer pays anymore. There are many other incentives involved, such as survey scores for luxury brands or mix of models sold (sell X of a model that isn't moving and we'll allocate you Y of the really hot model you can sell for MSRP because they're in demand).

The purpose of this system is partially to obfuscate the real "invoice" price so buyers searching the internet (or services like Edmunds) can't accurately price the car. It also allows the manufacturer to exert more control over dealers.