I actually had a little talk with Jeff(Rainwalker) just the other day, and he came up with these possible reasons:
1: to make blood and sap run off the blade, and not on to the handle.
2: to ease sharpening at the base. Much like a choil.
Also some ceremonial reasons
3: it is a symbol of a cows foot
4: it is a symbol of a cows teat
Cows are sacred in Nepal, and to the Hindu in general, so therefore the symbol tells, that the kukri is not to be used to kill the cow.

Makes sense to me, as I had wondered about it also.