The hypothesis that breastfed babies are at greater risk is not unthinkable.
First of all, hemorrhagic disease is rare, so that even if some babies died
from it, most did not.  Second of all, we live in a society which is
paranoid about cleanliness.  Vitamin K is made by certain bacteria in the
gut, which are growing happily in formula milieu.  They don't grow in
breastfeeding milieu, unless the baby is exposed to lots of bacteria (as in
preindustrial societies).

Also it is true that there is more vitamin K in colostrum and that many
breastfed babies don't get the colostrum very well.

Jack Newman, MD, FRCPC