I'd argue that all of those photojournalism shots would still be incredible even without ANY background. They're stunning works in their own right.
That's why I wrote that there will be lot of different opinions and I just wrote mine
I simply don't think the shot with Ali and Frazier would be so praised is there were no Ali and no Frazier but they were some unknown boxers. Yes, the photo is great, but I wouldn't call it incredible without capturing THAT moment. But that is what photo journalism is all about, so no offence.
Excellent topic. The boxing photo is actually Ali vs. Sonny Liston. Ali had just landed the famous "Phantom Punch" which was so quick that many of those in attendance didn't see it, and no photographer captured it. It's a fascinating story, and for more information, see Wikipedia Muhammad Ali vs. Sonny Liston.