That's because Taurus has Caleb Giddings, when Kimber designed the K6 they consulted Grant Cunningham and Mas Ayoob, and the Ultimate Carry J-Frames came directly from discussions here on P-F.
Ruger and Colt haven't consulted anyone with knowledge about concealed carry revolvers. Because both companies think Wiley Clapp is the smartest guy about carry guns. Don't get me wrong Clapp had good ideas, but nothing clean sheet in the designs.
And the UC guns are basically Lipsey's guns with the manufacturing subcontracted to S&W. I have no knowledge about it, but one might suppose that if S&W had said "nah", that Lipsey's could have gone to Ruger and commissioned a special run of LCRs.
If we have to march off into the next world, let us walk there on the bodies of our enemies.
Persuaded by all the hype (and considerable logic) around the Lipseys UC earlier this year I decided to jump on the .32 train a few months ago. But when I was at the LGS my gut told me to order the LCR .327 over the S&W. Ive owned a .38 and .22 LR LCR for over a decade with no problems whatsoever. The 327 has been equally reliable so far. With .32 S&W Long wadcutters its as much fun as the .22.
The three inch Viper in 357 will have a place in the den at my house. Does the viper have the replacable front sight like the King Cobra? Haven't seen the muzzle view of this model.
Building on the above:
The original Viper was an aluminum-framed duty revolver. That made sense when armed professionals still carried revolvers. If you carry a gun on your belt for your job, making the gun lighter has real practical benefits. But now, most revolver-buyers are collectors. A small minority are serious shooters. Making the King Cobra lighter in any meaningful way would require a lot of re-engineering and I don't think there's much of a payoff.
So sure, let's just release a half-lug version and call it a lightweight carry version of the King Cobra. I'd bet it was a relatively minor change in production, and it's just different enough to get some people to buy it.