I have heard significant differences between IC's in the critical line-stage to amp link with Audio Research, CAT, BAT, Aesthetix, Aria/Counterpoint, to name a few products. Are you claiming that the designers of these products are not competent to "control" the cable?
Actually I was restating something Ralph Karsten restated in this thread:
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1276356977&openflup&531&4#531
It is 8 paragraphs into the response if you include the numbered paragraphs.
Personally, I think Ralph has been on to something for a while. There is some credence to supporting the 600 ohm standard in balanced designs. Not many manufacturers do. This does not make them incompetent, but it does allow the cable to exert an influence on the signal. As for single ended designs the ability to design components to control the cable is more difficult. As Ralph states in the first sentence of this response to me in another thread:
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1276356977&openflup&537&4#537
Driving a load of less than 1000 ohms is not an easy task. So it makes sense that in single ended designs you could more easily hear differences in cables.
FWIW, I hear very little difference in cables in my system these days. I've sold off all my Stealth and other uber expensive cables and am running very modestly priced cables in my system. There's not much I'm missing IMO. Allowed me to to put more money in my components as well.