Hybrid (Silver/Copper) cables: do they make sense?

I see where Kimber makes the Hero cable in three versions: There is a one with all copper conductors; one with silver; and one (Hero HB) that has a silver conductor for the "hot" and copper for the ground. I wonder: why is it important for electrons to ride into the amplifier on silver wire, but OK for them ride back home on a mere copper ground wire? Seems to me that both legs of the circuit are equally important.

It's sort of like this: someone builds a posh hotel for people with BMWs and Rolls Royces. They pave the entrance driveway with expensive Italian Travertine tile. The exit is a gravel road. (OK, maybe asphalt.)

Get my point? Does it make sense to upgrade one conductor to silver, and leave the other as copper, in the same circuit? What am I missing, here?

Dip in (and then out) HERE