How do you figure 80% Canon?

These are percent scores, so if your 80% calculation is 3/5 in the top 5 plus 5/5 in P&S = 8/10 = 80%, that's not valid. You can't 'add' the two graphs because there are no raw numbers. Since there are no P&S cameras in the top 5, there's no way to know the relative totals are.

Three of the top 5 are Canon, which is 60%. If you ignore the iPhone 3G then 3/4 = 75%.

Also, that's just the count in the top 5...note that rank order is iPhone 3G > Nikon D90 > 3 Canon cameras. If you look at just 'today' (the right edge of the graph), and add it up, there are about twice as many users of of the three Canon dSLRs combined compared to Nikon D90 users.

It is clear that Canon dominates the P&S contributions to Flickr, and also clear that overall the Canon brand is better represented on Flickr than Nikon. But, Nikon tops Canon with the most popular individual dSLR model on Flickr.