I belive that katate dori was the response to nage holding a tanto or sword. Many of the open-hand technique that are taught in my dojo, as well as many dojo in ASU, cross over to bokken, jo, tanto....ect. This is taught to help with maai and judging the intent of uke's attack. Many of the hand/wrist grabs were also developed to prevent nage from drawing the sword. If uke is strong, sometimes the only way to draw your bokken/sword would be to use
tenkan, or ushiro movement.