From his biography, the turtleneck was kind of an accident:

> “So I called Issey [Miyake] and asked him to design a vest for Apple,” Jobs recalled. “I came back with some samples and told everyone it would be great if we would all wear these vests. Oh man, did I get booed off the stage. Everybody hated the idea.”

> “So I asked Issey to make me some of his black turtlenecks that I liked, and he made me like a hundred of them.” Jobs noticed my surprise when he told this story, so he gestured to them stacked up in the closet. “That’s what I wear,” he said. “I have enough to last for the rest of my life.”

I wonder if Issey thought the turtlenecks might be the Apple uniform, and that's why he made lots.