Doug, I remember years ago your telling me about a conversation with Joe Weed
http://www.joeweed.com/studiopages/highlandstudio.htm where he said recording quality was something like 90 percent performance, 5 percent mic placement, 3 percent instrument, and 2 percent everything else (mic choice, preamps, a/d converters, etc. etc.)
The trouble with your demos is that the 90 percent is so darned good the rest doesn't matter, at least as long as the mics are pointed at the guitar.
Fran