On the subject of ticket machines ....
I went to see my mum the other day and instead of buying my day return ticket from the ticket office at my local station, I waited until I got to Liverpool Street. I tapped in my requirement and the sum of £30 came up. I asked a member of staff why £30 was coming up rather than the £20 that I usually pay. I explained that I have a Freedom Pass (which allows a discount but this still doesn't account for the £10 difference) and he said "Oh, you can't do it on here then, you'll have to get it at the ticket office" - which I did, and paid the usual £20.
I realise that this was for overground, rather than tube, travel. But it did make me think that machines are all very well but they are inflexible and you can't ask them questions.
I also think that in an almost deserted station at night, someone sitting in a ticket office provides some sort of reassurance. And what about people with poor eyesight, people with a learning disability, or elderly people who are not so comfortable with technology?