To clarify: Forestry, the mod that has bees and trees and all those other things it has, also added butterflies awhile back. The same mod, not an addon or spin-off. What the end goal will be is anyone's guess but you buy into having butterflies in your world simply by adding Forestry. So your last post about 'people not using this mod' is missing the point at best. You already are using it. New feature X is in development is all.
ExtraBees/Trees/whatever-Binnie-does-next may add to or modify the uses of the things initially created by Forestry. If he has a future mod related to butterflies I'd imagine it would expand on the uses that SirSengir has for them in the first place in the same way the other 'ExtraX' mods currently do.
Just take a second to educate yourself about the things you want to talk about. I swear it will help.