That is one part of it. The other part is that there are hidden costs to automation.
Sure you get rid of the minimum wage jobs, but now you have to pay maintenance men a bit more to go out and fix them when they break, you will have down time issues too. You will need someone there to report when it breaks as well, unless it uses GE's predix(though i believe GE is hyping this wayyyyyyy to much).
There are network costs too, and security costs. One of the reasons why you see the push against cash in society, is it is expensive to pay the armored cars to collect the money every day. So the businessmen(who are an extra level of stupid, i know because i am one) believe it is cheaper to switch everything to cards.
So you get a lot of network problems: you have to make it secure, you have to have developers there to fix bugs in the UI on the kiosks and other places, you have to be updating due to security flaws. The list is huge.
Sure, you save money on minimum wage labor, but now you have more costs then you anticipated. Then there is what you said, customer service. What happens when the customer changes their mind and wants a refund? what happens when it is an elderly customer so you should take her tray to a table for them?(chick fli a does this)
From a business analyst standpoint this is a huge undertaking, and my end in utter disaster. I do hope it succeeds though, as the customer service in fast food sucks for everyone involved.