if you click on the "dynamic range" tab, you will see.
Compare cameras
i know alot of people feel weird about DXO, but i think they are doing a good thing.
as you can see, the K20D starts off with a bit over 11 stops of DR, which is more than enough for most situations, even on a sunny day.
then we start going downhill, and FAST
by ISO 1600,and 3200, pentax drops to ~8 and ~7 respectivly. All of a sudden you start to FEEL it, particulary when the DR of the scene goes up (such as a dark street with glaring street lights with light absorbing asphalt and reflecting windows) So you end up with having to sacrafice the dark areas for the highlights... and you FEEL IT, particulary when the blackness exhibits clear banding and blue dotted noise
the 5D and Mkii are a stop and a half better than pentax at 1600, by 3200 it approaches to 2 stops.
two stops of DR in the dark is alot, forget even about the noise, because its not a fair comparison
pentax gives you blackness with noise, while the canon will give you SOME information with noise, hence the perceived decrease in noise.
You can, ofcourse, make the Pentax work, i have done it many times, but the canon just makes it so much easier.