Having never been much interested in the subject, as I mostly shoot shaky street in which diffraction is the least of my problems (among other things, I'm usually shooting wide open, or close to it) I don't know the math or the technical stuff about diffraction. I can say that a friend has done serious work in this area and has said that human eyes can detect very tiny differences in sharpness when comparing prints side-by-side, but has also said that m4/3 cameras and lenses can make excellent prints at fairly large sizes, because you're not often comparing those side-by-side with sharper prints. In other words, sharpness has a psychological dimension as well as a technical one, and the psychological aspect is as important, and probably more important, as the technical one. A 24mp shot can look absolutely sharp at a large size, and while a 50mp shot at the same size will be technically sharper, it won't seem that way to a viewer who is not looking at both at the same time. You can do an enormous amount of research on what "pretty" means, and nail down 150 aspects of "pretty," but a pretty girl is a pretty girl.
Again, I don't know the math, but I'm curious about one aspect of Michael's article. He says that diffraction occurs because as the lens closes down, the amount of "disturbed" light at the edges of the shutter blades increases as a percentage of the total light hitting the sensor or film. But as the shutter closes down, doesn't the amount of blade exposure/interference also decrease? Or is it that it just doesn't decrease as fast as the overall area of the shutter opening?