Yep. When I’m frustrated on the phone with a rep, I always make sure to say something like “I understand this isn’t your fault, but I’m very frustrated with X.”

It seems to ease the tension a bit, anyway.

Angry customers aren't at fault. If all customers are mad as hell when they call, then the company will have to start paying better wages to keep customer support staff from quitting, and they'd rather fix the problem before doing that.