A "natural right wing" is traditionally described as someone plays right wing and shoots righty. When Alex Ovechkin, for example, plays right wing while shooting lefty he's playing his "off wing". Nash might be a better and more effective player on RW, but he's not a "natural right wing" - he's a guy playing his off wing.
Furthermore, it's much easier to defend and attack on your natural side because of your proximity to the boards. If you've played, it's really hard to clear the zone on your backhand if you're playing on your "off" side. It's hard to make a pass with your backhand. The biggest advantage to playing on your off side is having a better (closer to center) shot if you happen to be open in a scoring area like that. Nash isn't physical enough down low and routinely takes shots from the slot out on his off wing.
But, you've got MSL/Kreider/MZA/Nash as your top 4 wings and so do I. So someone is playing out of their preferred position.
It's always been my understanding that "natural" simply refers to what the player's most familiar / natural position. If it simply meant that a LW shoots left, and a RW shoots right, then the term "natural center" wouldn't exist.
A "natural LW" is simply a player who is most effective in that position and has played most of their career / feels natural / most comfortable in that position.
As far as goal-scorers go, the majority of wingers play on the "off-wing": lefties on RW, righties on LW because they have a better shooting angle and their forehand is open to the middle of the ice, especially for one-timers and snipe-style wrist shots.
Players who aren't goal-scorers (bottom-6 checking role, defensive players, grinders, etc) might be more likely to play on the LW as lefties and vice versa. Defensemen (at even strength) typically play on the same side as they are handed so that they are on their forehand along the boards.
The bottom line is that Nash has played significant time on both wings throughout his career and been successful/effective. Zuccarello has also shown the ability to play the left side without losing any effectiveness.
One of Nash/Zuccarello will be a LW in the top-6.
Nash fits perfectly in Pouliot's spot because he's the same body-type, skating stride, and is better at just about everything both offensively and defensively. It would be a seamless transition for Brassard and Zuccarello, and Nash would benefit from playing with two guys who are already on the same page. Furthermore, Brassard and Zuccarello are our best down-low cycle players which works perfectly for Nash's bull-to-the-net game. Nash doesn't want to carry the puck into the zone. He wants it off the cycle so he can use his strength and reach to come off the wall or out of the corner and bull his way into open space or to the net to create a chance. That's perfect because Brass and Zucc like to carry the puck into the zone and then look to make a play or cycle to keep the play alive.
And like others have said, AV likes his combos: Kreider+Stepan, Brass+Zucc.
That's why
Kreider Stepan St. Louis
Nash Brassard Zuccarello (or Zuccarello Brassard Nash)
Hagelin Miller/Lindberg Stempniak
Glass Moore Lombardi/Mueller
makes the most sense in terms of chemistry, continuity, balance, and slotting everyone in roles/spots they are capable of succeeding in.
Putting Miller with St. Louis (as some have suggested) is asking for Miller to overthink and defer to St. Louis and force plays. Putting the rookie center with two smart, responsible two-way players in Hagelin and Stempniak allows him to play his game and focus on simply playing by instinct and not overthinking / trying to do too much. Not to mention that St. Louis's ability to make his linemates better should be maximized with our top players, and vice versa, not a rookie.
