We have a fleet of 300+ late model cars, and I know we don't replace the rotors even close to every time we change pads....our rules require they be kept within manufacturer's specs.
I just called our head mechanic to ask him about it. We typically keep cars around 100K miles, and he said a lot of them leave with their original rotors still within spec. He agreed that the way they make rotors now isn't as good, and they don't have as much extra meat to start out with (so turning them often isn't possible), but said they still don't have to mess with them often. Sure, you get the occasional pad failure (happened to one of my assigned cars), or they get warped because someone gets crazy with an impact wrench, but those problems aren't the rotor's fault.