Mitch2-
One of the manufacturers who posts here, has said Romex would actually make a high performing power cord but it would not meet electrical codes for that purpose.
We talked about this some in the Romex to your Amp thread. here is what I posted there. It still applies here.
Electronics and power cords do not need to be UL listed. Certification is an optional process that costs $5,000-15,000 of dollars per model and is only good for 5 years. The only reason large manufacturers do this is because many retailers and contracts specify certified products only. Clearly very few (if any) boutique power cables and audio components are certified.
There is nothing wrong or illegal about solid core power cables.