I may be misunderstanding your argument, but I think the parent argument still applies whether you are getting served by a human or being served by a machine which has the same "one checkout at a time per person" kind of bottleneck that a human has.
Edit: The "scan your own cart" model is a more compelling counter-argument than the self checkout machines currently at Wal-Mart, as this can accommodate a much higher throughput.
Um, Walmart and most major grocery stores already have self checkout areas. So “wait in line to get served” isn’t quite the comparison. Most companies will give zero fucks about adopting this unless it becomes the expected norm.