Just because an airplane has a really nice autopilot doesn't mean it shouldn't be nice to fly manually.
If you assume the purpose of a car is to be fun, and that speed is not directly correlated to fun, then it's entirely reasonable to say a manual transmission, a fun and engaging way to interact with a car, is still a very necessary option.
My brother in law got an f10 M5 and I had a good run around an airport and then some in it, and it didn't do much for me. Very fast, but a bit boring. The DCT kept getting in the way.
"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams