If you go to the basement of the Nat History Museum in NYC they have (or used to have) this display of specialized traditional Chinese work knives.
The Chinese of late dynastic times (up to 1911 or so) were very fussy about using the proper knife for a specific task. That is, if you were gonna castrate a pig you'd better use the knife designed for pig castrating, etc.
The broad leaf shape and its variations are often associated w/food preparation. The broad blade allows for a very shallow edge angle and good control when using off hand fingers for positioning on straight cuts or chops.
The general utility leaf shape of the Spy/Lum comes from a southern Chinese (Cantonese) design and was likey adapted, in dynastic times, from some type of food preparation blade.
The northerners, generally speaking, prefered straighter and narrower blades for utility. These were often sheathed in a trousse that was cliped by a hanger to a belt or sash. The trousse usually contained a pair of chopsticks, "ear spoon," tooth pick and whatever else they wanted to fit in it.
Of course this is sort of a general breakdown. Knife types and usage varied by provence and not just a north/south division. A lot of Chinese utility blade designs probably depended on how much it actually had to do and was a function (like anywhere) of the type of food and fuel available in a given provence as well as the crime rate, etc.
[This message has been edited by booshank (edited 12-17-2000).]