Boy you've got that right! In film days ISO 50,000 film was unthinkable. Consider this quote from the Wiki article on film speed:
"Some high-speed black-and-white films, such as Ilford Delta 3200 and Kodak T-MAX P3200, are marketed with film speeds in excess of their true ISO speed as determined using the ISO testing method. For example, the Ilford product is actually an ISO 1000 film, according to its data sheet. The manufacturers do not indicate that the 3200 number is an ISO rating on their packaging. Kodak and Fuji also marketed E6 films designed for pushing (hence the "P" prefix), such as Ektachrome P800/1600 and Fujichrome P1600, both with a base speed of ISO 400."
That means that the fastest B&W film commonly available was actually pushed ISO 1000 film, and the fastest commonly available color film was actually pushed ISO 400 film. I've used all these fast films - and frankly, they didn't look very good. The D800 produces excellent results at ISO 1600, and quite acceptable results at ISO 6400 - much, much better that any film I've used at even 1/4th the speed.
In the early days of film speeds were around ISO 12-32. Later, good ISO 400 films appeared because of technological advances. Technology marches forward and people remain interested in pushing boundaries.