I thought oneguy's first picture was interesting - if you look at the green cloth and especially the pink cloth on the back, you can see much more detail in the K-X picture. It is only the one red cloth that the K-x seems to have less detail than the Nikon. And with the 2nd and 3rd pictures you can also see more detail (look at the letters in the second one), though also more noise. As Hards said, Nikon has always had more aggressive noise reduction while sacrificing detail.
Some people will prefer Nikon's noise reduction over capturing all of the detail possible. I shoot lots of macro so I prefer to have the detail. If I want less noise, I'll use noise reduction software and decide for myself how much detail I want to lose to reduce noise. The only thing that the pictures convince me is that the K-x struggles with bright reds (if it's like the K20, changing to natural over bright or turning down the saturation a bit makes a big difference in how the camera handles reds).
I also agree that you probably wouldn't notice much difference in real world conditions.