Isn't that what they did with the smartphone market? The big difference is that the iPhone is a computer running OS X -- all things Apple has huge experience with. A car is something they have no experience with.
Would you argue the most significant part is that big tablet in the middle or the combination of the wheels, steering, axles, interior upholstery, steel frame, aluminum body panels, battery, etc?
Apple hasn't manufactured anything larger than can be easily Fedex'd. It seems like calling the Tesla an iPhone on wheels misses nearly all of the significant details.
Musk has made the point that a lot of that stuff can be purchased from or outsourced to third parties. Which is what the traditional car companies now do. Which is what Tesla does.
The traditional manufacturers maintained their expertise in engines, but, ironically, that's one thing that Tesla had absolutely no use for anyway.