I don't believe any manufacturer would deliberately set out to design a gasoline pump or any kind of measuring device that would skew what it delivers. Certainly these companies live and die by their reputation and by their technology. If word got around that they were manufacturing devices that were not the best technology available in the marketplace, there are always competitors.
As to why there's a bias, I really can't speculate on that. There may be many factors, such as wear and tear—they are mechanical. I really am not in a position to say that we have done a detailed study as to why these devices may wear in favour of the retailer more often than the consumer.