Nigh on every single time someone reports on a cable melting eventually it comes down to the user not plugging in all the way even if it's as little as 1mm, Very rarely is it an actual fault with the cable.
When a design is prone to causing user error, the fault is on the design not on the user!
I've said this before here and i'm saying it again it IS all NVIDIA's fault! They've designed a cable that goes against ALL previous knowledge and experience and while telling everyone about it, as you suggested, is damn sure the least they could do, it is not enough! It would never be,
I've been building PCs for the last 15 years or so and if I was one of the first persons to get this conector I would probably not plug it all the way in! I'm to the point I don't even look at the conections I make I know how much force I should use on them and I make sure to apply more than that, but these 12pin conectors require easily twice that force, it's enough to make me feel unconfortable applying such force from fear of breaking a solder joint.
And that's all for nothing because the common 8-pin PCI-E conector can easily handle this amount of power, they didn't need to add more pins, neither did they need to make it smaller, simply changing the keying on the pins woudl suffice to separate the high-power 8 pin to the normal 8-pin, they coudl've revised it just a little to further increse it's power handling capability as to avoid exactly this issue, because part of the reason the 8-PIN conector is so resilient is that while it is rated for only 150W, it is capable of handling 800W, so even if the conection isn't perfect it will still most likelly work fine as it is being operated well unders it's actual engineered power capacity.
What NVIDIA did was create a conector that's built to handle exactly 600W and then rate it and specify it for 600W meaning any small defect or user error, or simply variance will cause it to fail! That's really, really dumb and bad engineering. While the commons 8-pin is really really smart engineering avoiding issues even in the face of user error.