Overall I agree with your sentiments, but I have to address this next part.
Note--I also generally hate the overemphasis of the importance of the "right-handed shooting defenseman" that goes back to Howson. Take a look at the Ducks team that won the Cup. Unless you think Joe DiPenta was the key to the backend, they seemed to do fine with most of their guys shooting from the left.
I can't find any evidence of a handed bias under Howson.
LHD drafted: Olson, Weber, Blomqvist, Moore, Reilly, Murray, Curcuruto (7 total)
RHD drafted: Goloubef, Delisle, Savard, Larkin, Prout, Madaisky, Archibald (7 total)
If you break it down by round, the two first-rounders (Murray and Moore) are both lefties, as is 1/2 second-rounders (Weber), so there doesn't seem to be a bonus given to handedness.
Among defensemen he acquired:
LHD: Hejda, Tarnstrom, Tyutin, Backman, Paetsch, Lepisto, Nikitin, Johnson, Lebda, Erixon (10 total)
RHD: Commodore, Roy, Jurcina, Stralman, Rivet, Guenin, Wisniewski, Martinek, Aucoin (9 total)
If you compare the playing styles of the draft picks and the acquired players (whether free agents or in trade), there's nothing to support the idea of a bias toward either RHD or LHD.
So there's two possibilities.
1) It's entirely a media construct. Considering the way that the collective sports media treats inane blather as holy scripture, this is very possible. Or...
2) Having a decent amount of balance on the roster and in the system is exploiting a bias that doesn't exist everywhere, but certainly exists somewhere. Good baseball GMs have traditionally loaded up on middle and short relief pitchers of both hands, knowing that a team that platoons heavily will normally be guided by a manager who feels a compelling need to have as many options out of the bullpen as possible. I call this "The Tony LaRussa Effect". Knowing that the bias exists elsewhere, they're able to command a premium in the trade market for a guy who may be completely useless if not for what hand he throws with. The Indians were on the bad end of this when they traded Brian Giles (just entering his prime) for Ricardo Rincon, a fat reliever from the Mexican League who thought a strikeout was a pastry.
If someone else is willing to bump their third-round offer up to a 1st simply because the player they're picking up shoots from one side, that's something that needs to be prepared for. Conversely, if a GM regularly talks about handedness being important and thus is able to drive down an offer for a player he wants on account of making the other guy think he possesses that bias, then it might as well be talked about.