Hmmm...I'm not seeing anything either. I suspect maybe the only difference is that DK made the same way may just be a little smaller. I saw on Rav that it might be on the big side so maybe that is a good thing?
When asking questions ALWAYS post the name and a link for the pattern if you have it.
Using either DK or WW gives you the option of two sizes, one a bit smaller than the other with the same pattern instructions. The notes suggest the DK for a chemo cap which would need to be a bit smaller.