The Nikon F was the most influential SLR of all time and should have been included. It was the workhorse of photojournalists for over twenty years.
The Argus C-3 was the amateur 35mm camera of choice for budget minded photographers and sold in great numbers.
The Graflex 4X5 was the first successful SLR and was used by professionals and photojournalists.
The Speed Graphic was the press photographers' choice for the first half of the 20th Century and was replaced mainly by the Leica M3 and then the Nikon F.
In truth, the top 20 list probably should have been the top 100 list. I would have compressed all of the models listed of the Rollei and all of the models of the Leica into their own headings as each were respectively improvements of pre-existing cameras.