Albeit the minimum amount of respect Ken receives from the internet photography community, his article that you linked explains it very well.

Here's the summary:

"Excuse me, but do you see anything significantly different among the DSLRs? The only thing I see is more aliasing with the Canons, but the same noise. I have a sneaking suspicion that the people who start these old-wives' tales start them from what they read in a press release from a camera maker, or an article written by someone who finds it easier to repeat the press release instead of running his own tests. These shots took me a couple of hours to design, a couple of hours to shoot, paying attention to maintaining the same focus and conditions and settings for all cameras, and a week to format into this web page with all the little crops all labeled.

Any simpler effort introduces other variables which skew the results. I believe it is these other variables which lead to the old wives' tales of Canon or Nikon having better high ISO performance. Once someone expects a result, they (and I) will tend to see that result. It's simple psychology.

I see the same noise and the same real resolution from each DSLR. Above the real resolution, I see much cleaner response from the Nikons (just gray in the middle of the star target) and aliasing from the Canons."