Is it all that different from selling phones?
Apple has "dealerships" that sell phones, and provide service to phones in the form of the stores. They'd obviously need a separate network of car dealerships to sell and service cars, but Tesla was able to set it up with a fraction of the resources Apple has available to them.
Selling phones means dealing with various federal regulators, and while the regulations around cars are obviously far greater, it isn't something Apple is unwilling to do. There are insurance and other hurdles unique to cars, so I don't mean to claim they're the same, but Tesla showed how easy it is to start a car company from the ground up, and they have a fraction of the resources Apple has at their disposal.
I would agree with those who suggest that contract manufacturing cars like they do iPhones is not really feasible, so they'd have to own and operate the factory themselves. While everyone assumes Apple would never make anything themselves, they ALWAYS have. They have been making iMacs at an Apple owned and operated factory in Ireland since Jobs returned. The iPod was their first real foray into contract manufacturing of an important product, but there are good reasons why they made that choice - they were nearly broke when they started selling it and setting up their own factory with a capacity large enough to meet demand was not really feasible.
Since the relationship with Foxconn worked out well for the iPod, they continued it with the iPhone and iPad. Steve Jobs was heavily involved in the planning and design of state of the art factories for both Apple and NeXT, so there would be no way for someone within Apple to oppose manufacturing cars themselves by saying "that's not what Steve would do".
If anything, licensing software instead of making hardware is totally against Apple's corporate identity. They've become the most profitable company in the world by controlling the whole stack, not carving out a piece for themselves in something someone else sells and supports. There are a lot of companies, both inside and outside the auto industry, working on autonomous driving technology. There will be a few winners who get there first, but eventually a lot of players will, and the capability will become a commodity and Apple has no interest in a commodity market. Maybe they have an easier to use more intuitive interface for dealing with the car, but as with the iPhone even if they managed to get there first, they can't stop others from following their lead.
I think they have to make cars if they want this project to succeed long term. And I find it hard to believe that the massive amounts of money they've added to R&D can be around simply doing autonomous software. Either they have some other big projects in the works that have been kept more secret than Titan, or the rumor about them not making cars and just selling software is untrue.