It doesnt - if you read it it says that the shots were all taken at 1/250th and the aperture changed to match the increase in ISO... the aperture changed the DOF...

Nice link tho kort, explains the relationships nicely  (although the DOF - ISO relationship could have been better explained to be fair)

I remember reading an article which had a graph of noise to signal ratio (ie clarity of exposure) mapped against ISO, the graph started at 100, went up at 125 then down at 160 then up again at 200... So i use 160 as a default as i get 2/3rd or a stop extra light for only a fraction of the extra noise that 200 would cause.  This was only for a 30D tho - i'll try and find the article when i have a bit more time...

"In every colour, there's the light.
In every stone sleeps a crystal.
Remember the Shaman, when he used to say:
Man is the dream of the Dolphin"

Rich Meadows Photography