I think the "right shooting defenseman" thing has tended to get overblown over the last three years. Nothing about being a right shooter makes a guy better, or more deserving of a roster spot. It's a characteristic that, all things being equal, you'd like to have a balance of.
For instance, Marchenko and Smith were a better pair last year than Smith and Zidlicky. In one instance having a righty worked, and in the other it didn't make much difference. If forced to choose, I would rather have seen Smith with another lefty (Ouellet?), or Zidlicky with another righty (Marchenko?), rather than those two together.
The lefty righty thing is based on all other variables being equal. If you're trying to find a partner for a lefty, and you've got two good guys with similar skillsets, then pick a righty. But if one guy is a mismatch in every other way, but is right handed, don't give him the spot based primarily on that.
Just my 2 cents.
When you consider that over 70% of NHL Defencemen shoot left handed, It certainly helps to have a Right Handed shot when it comes to bubble players in the pre-season and/or free agents in the off-season. No, you aren't cutting Nick Kronwall to make room for Nick Jensen, but the theory of having an equal number of each stems from basic (positional) fundamentals and not just because it's simply good to have a balance of both.
Ideally, you would like to have 3 LH and 3 RH Defencemen at all times - because it's much harder to play the opposite side as a Dman than it is as a Forward...Alot of Forwards actually prefer to play their off-wing because its beneficial in most scoring area's around the slot.
As a left handed Defenceman playing the right side, it is much more difficult to retrieve the puck off the boards and move it quickly when sustaining offensive zone time... At NHL level, retrieving pucks on your backhand at the blueline to keep the zone (especially at even strength) typically gives the opposing team too much time to make a play. It's also harder to "play catch" and set up your offence at the top of the zone if both Dmen are Left Handed, and opposing teams will key in on this. Not to get too crazy, because we are talking about the best in the world here... but it's also easier to pivot, and force opposing forwards to the outside when you are playing the correct side.
On the PP, it's also beneficial to have both shots out there (think Lidstrom, Rafalski) - because once possession is established after the faceoff is won, the Defencemen can "switch" and create two shooting lanes as opposed to just one. Doing that, also creates room down low because the shorthanded team has to send 2 guys high...
It's not really overblown, and although you aren't arbitrarily a better player based on the fact you shoot right handed, you can certainly put your team in a position to be better. This is why they command more money every off-season, and more demand every trade deadline then left handed shooting players.