The correct thought experiment is: having bought a car from Ford, you examine it carefully then purchase all the raw materials yourself and assemble an identical duplicate for your wife.
In doing so you save whatever markup Ford places above and beyond their marginal cost.
Asking whether this is morally okay is the true issue.
But I agree that your experiment boils down to the problem I am pointing to, and it is better because it is a very real problem that we see every day (e.g. in China).
It does, and the cases are not comparable. Leaving an empty space (plus marginal cost) where the car used to be requires the original owner to expend time and effort to replace it, and they have opportunity cost as well. None of that is true of the digital example. To be a fair comparison you'd have to leave an atom-for-atom identical replacement for the car (or more accurately, take an identical copy and leave the original) and I doubt as many people would judge that unethical.