I've blogged before about the nuances of "you're welcome" vs. "no problem" as a response to "thank you".
But reading this story from Not Always Right gave me some sudden insight on why the "you're welcome" people don't like being told "no problem": they want it to be a problem!
They seem to be interpreting "you're welcome" as "you are welcome [in the sense of "entitled"] to impose upon me by making this request of me", and see a "no problem" as implying that they are not entitled to that. "No problem" is equalizing, "you're welcome" is subservient.
I use "no problem" specifically because it is equalizing, in an attempt to neutralize the burden of gratitude in the other party. I'm saying "It's okay, we're cool, you don't owe me any gratitude, I'm not putting this on your tab." This is what I like in customer service and in life in general, so I try to give it to others.
It makes me feel welcome in the literal sense, the same way I'm welcome in, say, my parents' home. I'm totally allowed to walk in and fix myself a drink and rummage through the fridge. In a customer service context, it makes me feel like they're giving me good service because I'm just as cool as they are, not because I'm above them. Because they like me, not because they are obligated to serve me. They're saying "Hey, it's you! How are you doing? Do you want a coffee?" rather than doing their job and rolling their eyes at me when I leave. And, while it is totally their prerogative to just do the job and roll their eyes at me when I leave, I'd much rather have them like me.
But the "you're welcome" people don't seem to care about that, they seem to prefer to be treated with deference, liked for their position rather than for themselves.