Greg,
I was surprised too. My guess would be ease of starting. As soon as the rig is started and brought off idle, the vacuum advance does bring the timing BTDC, and don't forget that the centrifugal system is just hanging out waiting to get into the fray too.
Although initial timing might be retarded, for all intensive purposes, the engine runs most of the time advanced.
I think any shade tree mechanic would dial in some initial advance anyway...to hell with the shop manual, we want power!
Stuart
