Business does not adopt a change in technology unless it affects the bottom line in a good way. McDonald's didn't put in Kiosks simply because somebody invented a kiosk. They are a pure substitution of capital for labor because the ROI made it worth implementing them. To think otherwise is simply wrong.
Also, historical measures have nothing to do with future business plans. Substituting capital for labor is done with respect to current costs and what those costs are expected to do in the future. Saying that the minimum wage rate in 1938 was $0.25/hr has absolutely nothing to do with business planning today.
Even if McD's could get workers at $2.00/hr they would have still automated. The automated because they'd rather deal with machines than with human employees. There is no wage floor that would have stopped this from happening. It wasn't even a considerations.
This is the same as the steam shovel replacing thousands of ditch diggers. Their labor was no longer needed at any price.