So, why not add fluorine to the electronics definition of "halogen-free?" The main reason is that the environmental organizations such as Greenpeace are only targeting Cl and Br. Therefore, the electronics giants are simply making it easier for themselves. Why restrict an item that is not likely to give them bad press? It would be tough to argue that Fluorine is more enviromenmentally safe than the other halogens.
The concern with excluding fluorine from the halogen-free specification is that it is possible to use this as a substitute activator (rather than Cl or Br). F may make the flux more prone to corrosion and SIR issues.
I say add fluorine and make it more complete but that's just my two cents!