Growing up here in Texas, it's always been that slower moving vehicles move onto the shoulder to allow you to pass, especially in small towns. A friendly wave is given from both drivers. I've not seen anyone move over if they were going the speed limit though.
I feel your irritation, I do the speed limit most of the time even with my radar detector.
Hey, it tells me when the train is coming and emergency vehicles. I do love it when people impatiently pass me and my radar is buzzing like crazy! 