It's actually *right-shooting* defenseman.
AIUI, so as not to be weak on the backhand, hockey players are taught at a very early age to play with the non-dominant hand being dominant. Therefore (theoretically), the players who shoot right are actually left-handed, whereas the players who shoot left are actually right-handed. That's why there is a huge discrepancy in numbers regarding defenseman who shoot right-handed as opposed to left-handed. Since fewer people are left-handed, that translates over into fewer NHL defenseman who shoot right-handed. In other words (again, this is all just theory and not necessarily indicative of each and every player), right-shooting NHL defenseman are more rare because there are less peeps in the world who are left-handed as opposed to right-handed.
Personally, I think it's a crock. I'm right-handed and once attempted to shoot left-handed. I could do it, but there was little to no power to my shots. If Martinez (for example) was to switch from shooting left to shooting right (I'm assuming, of course, that Martinez is right-handed), I'll bet he could score 15-20 goals each season, EASILY, backhand be damned. That's just IMHO......