You are correct. In my experience, and the experience of my friends, quite the opposite is true: you must switch regularly to get decent rates. If you are only getting $5 off /month then you need to switch.
"I'd have to call every year to reluctantly get offered $5 off for a year."
I've asked people in retentions why they put me through this dance every year. I was told that this is just the system and that in the future I should just jump straight to retentions and not waste my time with the front line people who can't dole out the 'real' deals.
The whole system seems very wasteful to me, not to mention that I feel bad for elder, and less aggressive people who pay so much more then the rest of us. I wish they would just publish one set of (competitive) rates and be done with it.