You are right, it was right there for me to see. I must have overlooked it when viewing the pictures that illustrated the differece between 8mm and 10mm.
I was curious about this because I always find myself pushing the magnification limits of all of my lenses. More is always better for me in this regard. Not a necessity, but a bonus. It appears the Tokina at .09x (1:11.6) is the loser in this department.
I don't think this will be the deciding factor for many people, it is certainly a consideration.
At this focal length, I think the more relevant spec is not maximum magnification, but rather minimal focusing distance. Both the Canon and Sigma is 24cm, while the Tokina is 38.
With the large depth-of-field, at 8mm even at f4.5, my 7D actually reports subject in focus at about 21-22cm with the Sigma. That's from the subject to the plane of the sensor. The distance between the plane of the sensor to the tip of the built-in hood is about 15mm, so the subject is only about 7cm from the hood at minimum focusing distance at f4.5. If you stop it down, you may probably decrease it some more and still get the subject to be in focus.