I'm in an awkward generation that grew up to address people formally; your boss would never be Bob or Jane but Mr. Smith or Mrs. Jones, for example. For younger people, 'you're welcome' or even 'my pleasure' sound too formal and stiff, so they go with 'no problem' or 'yup,' which sounds rude to many people. FWIW, I always liked that a former neighbor of mine would respond with 'of course.'
Speaking of informality, I think the topic of automatically addressing people with a nickname has come up before. Not only is my nickname not what most people shorten my name too, but I really hate what they shorten it too. When it doubt, address people formally, until somebody says otherwise.