Does adding a point to the two-handed fighting style effect proficiency with the bow (or any ranged weapon for that matter) or is it with melee weapons only? I don't entirely understand the additional "fighting style" proficiencies.

<font color="lightblue">It should.</font>

No, it does not most probably. A simple check: Give ++ to the 2H weapon style and equip a 2H weapon. You will see "Critical Strike +1" at your personal screen. Now, equip a bow. The Critical Strike bonus vanishes. Therefore, the 2H weapon style does not affect bows most probably.

It doesn't - the 2H weapons prof applies to melee weapons only.

And in four posts, we go from a should to a most definite NO. :D