Actually, I can't view the first link, but in the second the canon lens seems to be brighter - not that I can really tell as the image is rather small.
But that's neither here nor there. The point behind an L series lens is not necessarily how much better it performs than other lenses, but the way that it is made. And I guarantee the L lens in this pseudo-comparison will outlast the nikon - being that I've used that nikon, albeit briefly. But that's not even the point. If you're the sort of person who only cares about how well you perceive the image quality vs. price, than you'll never find the need for a professional lens. Nikon has pro lenses too, you know.
When you buy a lens, the money you invest determines how long you plan to keep and use that lens. Technically, my AF nikkor 70-210mm f/4-5.6D outperforms both, and it's a 12 year old push/pull zoom with loose mechanics. It's still my best telezoom, and has lasted beyond any of the DX AF-S lenses I've had the misfortune of owning - except maybe my 16-85 VR, which I spent $500+ on.
Though I like him, don't let Ken Rockwell fool you about cheap lenses. Sure, he loves to plug his el cheapo lenses as the best for the money, but he doesn't use them ALL the time (and even admits to that). So if you're going for longevity, the more money you put on a lens, the better quality it will be.
Note: Your comparison isn't enough to convince me that this isn't just some rant about cost justification. You don't give the conditions under which the test was conducted. You don't share the cameras used - which have implications, you compare nikon vs. canon, and the differences in sharpness attributable between JPEGs of the two. And sure, the 70-200 f/4L isn't canon's best. For another $350, you could have the much better 70-200 f/4L IS, which is one of canon's highest rated lenses in terms of image quality. So it's true what they say, you do get what you pay for.