I did extensive research to answer the original question, it seems that all companies conducting Grand Canyon tours, from Grand Canyon and from Las Vegas haved pretty good records. All companies that I checked on have actually carried more tourists that they did not kill than ones that they did kill. Probably safer to do the flight than the drive up to the Canyon!
Keep in mind that this was not a scientific research project, but I do think the results were extreemly accurate.
Mark