It's possible that in this case the tickets were issued and one was left in the TVM▸ hopper. There's very little in the way of checks and balances once that has happened.
I agree. Leaving the ticket in the hopper (or anywhere else) is clearly the fault of the customer and I'd be happy with no refund being given in such circumstances. I do think that a refund in the case of genuine non-collection (ie when the computer knows that no ticket of that number has been printed) would be good customer relations.
I'm not a big fan of analogies with retail purchases
Maybe not but all passengers will have experience of retails purchases and an therefore expectation to be treated as well by the railway as by Tescos of M&S. Customers will use the retail sector as their benchmark of what is "fair"