This reminds me of a time when I was holding forth idly (as you do) about how some languages have an automatic response to 'thankyou' and some don't - in Italian, for instance, 'Grazie' is always met with 'Prego', and I think German is pretty similar with 'Danke schön' and 'Bitte schön'. English, I opined, isn't like that. Some of the people I was holding forth to were American, & they said that, on the contrary, English is like that - someone says 'Thankyou', you say 'You're welcome', no ifs and buts. I can only say that it's never been like that (to my knowledge) in British English; as Spleen said, you can reply to 'Thankyou' with 'not at all' or 'no problem' or 'cheers' or 'don't mention it' or 'it was nothing' or quite a number of other phrases.