i also belong to the himalayan imports forum, where the cho/kaudi debate comes up frequently. a recent thread->
Linky
the conclusion is normally 'no one knows why they have one, or why other nepali weapons do not, they just do'.
they are now a religious and traditional inclusion on the kukuhri's such that it is not considered a kukuhri if it does not have one. the kami's normally bless the new kukhri's in a mass ceremony involving sacrifice, so they are serious.
kukuhri cho/kaudi also come in a closed style rather than the more common notch:
examples:
so, the blood dripper/blade catcher theory falls a bit flat with those variants.