How would the woman have felt if the till operator had carried on a conversation with the till operator in the next aisle whilst serving her. Bet she would not have liked that alternative situation. Apart from anything you need to be concentrating on what the assistant is doing in case she makes a mistake (now my mind thinking of alternative ways of getting back at her, might have wanted her to scan a couple of things twice).
One thing I have noticed with mobile phones is mums pushing buggies. When my children were little I talked at them and then with them, when we were out and about. Now I see mum's pushing their buggies whilst holding long conversations with a friend rather than talking/interacting with the child.