I've been lead to believe that in the Warhammer 40,000 universe, untouchables - those who are psychic blanks, and act to cancel psychic powers - are very rare. However in two separate series the main character has a friend/companion/awkward love interest who is an untouchable.
I'm refering to:
Jurgan and Bequin, from Ciaphas Cain and Eisenhorn novels, respectively
So are they really that rare? Or is it just that they are a useful story aid?