I think the way it's percieved is that the longer a driver is with a company, the more per mile he gets - but the fewer miles THAT COMPANY gives him.
I'm sure it happens to some drivers - the question is, how much of it is brought upon themselves? How often do they get grumpy about 300 mile loads? Get a relaxed attitude about safety or delivery time.. etc. Maybe none, but we're unlikely to ever find out here.
I can't speak for other companies, but I know a couple drivers at my own who are pulling more than a few cents more than me, and have all the miles they can take. Once in a while they'll get caught in a short-haul loop for a while, but so far, a word to the DM is sufficient to take care of the problem. Either way, it's not a matter of ppm - it's simply a wrong place/wrong time issue. If I'd been in the area instead of them, I'd have had the same problem.