How do manual supercars achieve such high speeds (190mph+) with only 6 gears when it takes all 6 gears to get to 70 mph?

Though obviously a transmission would be a lot more complicated with more than 6 (or 7 or 8 gears like Porsche or some Corvettes) gears, and the car is obviously red-lined at Vmax, why aren't there more cars with a gear that is intended for these high speeds?Sorry for the naive question! via /r/cars http://ift.tt/2sNYFj8