I agree, Apple could skip a lot of ramp-up if they buy a car company. But, then, what are they bringing to this hypothetical scenario? Does buying an existing car company make it easier for them to bring some kind of distinctive iCar onto the market? If so, what do we imagine is the distinctive iCar-ness that they're bringing?
There are two things that I hear people say Apple is notably good at:
1. "Design."
2. Controlling a complicated end-to-end extremely high-quality manufacturing process.
For 1, I'm not sure I believe that there is a transferable organizational expertise between designing phones and designing cars.
For 2, I'm not sure I believe that there is a transferable organizational expertise between manufacturing phones and manufacturing cars, and I'm definitely sure that I don't believe that they can transfer organizational expertise to manufacturing cars if they purchase an extant manufacturing process/organization.