The difference between the kinds of film being discussed and digital upgrades is that the film didn't allow photographers to shoot in more environments and with higher quality. The difference between Panatomic-X 100 and Tri-X 100 were aesthetic. While those differences are certainly important, both were ISO 100, and both worked in the same range of lighting conditions. With digital, however, sensor upgrades allow photographers to take pictures they could not have taken with the previous generation of cameras. My last camera, for example, took great photos at ISO 400 and O.K. photos at ISO 800. My current camera looks great at ISO 800 and O.K. at ISO 1600. This constitutes an improvement in what I can shoot and where I can shoot it, which was less true for the film upgrades everyone's been discussing.