Earlier quoted context omitted.
> Late night in Stockholm train station, I bought one bottle of fizzy water and checkout added 30 seconds or so. This seems like a situation that would be improved for all concerned parties if there was a vending machine in the station.
Well, a vending machine would have limited inventory. Whereas you can buy a lot more stuff at a store. I was at Stockholm Centralstation and used the self-checkout there too -- it works fine if you have less than 5 items (which you typically would). The Co-op grocery store in Stockholm Centralstation also has self-checkouts but it's self-checkout is a lot slower when you have 20-30 items in your cart, and you have to…
You bought one bottle of water. You're not benefiting from the store. The store owner isn't benefiting from you using his store instead of his vending machine. Store customers aren't benefiting from you using the store instead of the vending machine.
If it works in the Shanghai subway (daily ridership roughly ten times the population of Stockholm), it'll work in the Stockholm stations too.