That may be it, but I think have a "workaround". Instead of "selecting by not commenting out"...How about making all the biomes not commented out "Snow" (or the one biome commented out). (I know that just aims to fix the "one-biome-selected" scenario, but I guess it could work for multiple splitting the others between the ones commented out for true balance. Either way, there needs to be a more aggressive way to select the biomes you want, rather than have them selected by the absence of "manual code manipulation". Most, I can assure you, don't unpack mods, modify them, then re-pack them. Thus "Mod Settings" are implemented for this sort of stuff.
That all being said...THIS is being worked on as we speak. Only so many hours in the day, y'know?
P.S. Was the code snippet you gave above in your mod or Alien Biomes' mod?