I was wondering the same thing and noticed that the vowels almost always feature in the top 10 and DVORAK has them all in one hand. yay..Infact, in a very casual observation, i think only 'r' seems to be the letter out of DVORAK layout.. I looked across languages though. Guess this makes me a DVORAK evangelist.:-) And to complete that image i will add this DVzine link.
http://www.dvzine.org/