That might explain it for North America, but my motivation was actually listening to the British TV presenters talking about the World Cup.

I'm not saying you're using it wrong, just that most people would consider it unnecessary in modern usage. Certainly with something in transition would make some people think it was needed in cases where others didn't. Or maybe it's making a comeback, I don't know. I can say that in context such as politics (there was a voter meeting I went to recently), probably a generation ago you'd have expected "de", but now you won't be corrected if you don't. Same goes for most contexts. Along with that you tend not to have a conversation about being "dus", which I've had several times down here.

And I'm only 2 years older than you. Just like you, I use it when I think someone wants to hear it. I think someone wants to hear it because they're of an older generation. How many days out of the last 7 have you heard it in a non-ceremonial context? How many interviews do you see it in? There was even a blooper clip last year of an interviewer who forgot to use it when addressing Prince Joachim. You wouldn't forget that if it was common.