That seems like a big liability for them... I'm sure some enterprising lawyers are already plotting a class action. Consumer buys car after test drive and loves performance, but it turns out performance was a lie. They may have to do a buy back.
The vast majority of consumers won't notice. Some will be upset, because They bought the car for the specs on paper just to feel cool. Similar to how the fanboi segment of consumers by video cards and computers and stereo equipment.
Yup, quite possibly thinking about bailing on the car sooner rather than later. I have no idea if this kind of thing significantly affects resale value, but I'm not sure I want to wait around to find out.