The factory is never going to give you the absolute best performance. Partially because they are trying to appeal to a broader market than say just the "1/4-mile guys". If they were trying to sell only to those guys, every car would be black, weigh 2000 lbs, have 500HP, no radio, no A/C, no sound deading, only a driver's seat, and a built in roll cage. It wouldn't be street legal and they'd sell 100 cars, not the 100,000 that they are targeting.
So, they compromise. Drop the performance a little bit, drop the price, up the amenities, offer some choices in trim/color/options/etc to appeal to a much broader market.
The other part of this equation is the aftermarket. No matter how good a factory makes a car, there will always be someone out there tuning it to be better. Look at companies like RUF and TechArt (they tune lots of Porsches). Hamman and Novitec (they tune a lot of Ferraris). Or even Hennessey with the Vipers. There will always be someone out there getting more performance out of a car than the factory.