Why manufactures don´t burn in their amps and ...

Most performance vehicles do require driving at limited RPM's for the first few thousand miles of seating the pistons. Porsche's is about 2000 miles. I would guess that manufactures don't break in audio gear because it takes 300-400 hours of constant running sometimes within the context of being within a system with a signal running through (speakers and amplifiers). Ultimately it probably just doesn't make economic sense. OTOH, I see no reason, given the modest cost of materials involved, for any high-end manufacturer to provide "better" power cords. Again, I'm sure the reason is economic in that the more they can keep manufacturing cost down the more appealing to the consumer, the better it may look in the face of competition, and the more potential profit. It's the kind of thing where if one manufacturer starts a trend, other's may follow.

Thanks for that, Ralph! That's the most concise and clear explanation I've read on the subject.

A couple of questions:

What accounts for a 3-volt drop across an AC cord? How does that happen? Is this an argument for shorter power cords? Is it all in material and design?

Why/how can one power cord dump more current at the peaks faster than another? Isn't this limited or affected to some degree by the power source (the AC), and how that source is delivering power? I think (perhaps erroneously) about the analogy of a hose delivering water - no matter whether the hose is fat or thin or obstructed or not, it will always be limited to some degree by the delivery of the water from the spigot. If the water is being delivered in spurts and fits, the hose will not change that.