I guess theres no real diffence in cables?
That's one of those questions that's harder to answer than it looks...
I am involved right now in a speaker cable project for a client which involves some very interesting theoretical work done by one electrical engineer pertaining to some odd features of low-frequency signalling, and discussing the engineering issues has made it clear enough to me that there are some hypotheses, where speaker cable is concerned, that are very much worth empirical testing.
But in general, I think it is fair to say that barring some truly odd and esoteric things being done, the largest factor by FAR in speaker cable quality is simply wire size. Because it's a low-impedance, high-current signal, susceptible to frequency-dependent losses that flow from the relation between the resistance of the cable (which is nearly flat across the audio spectrum) and the impedance of the speaker (which is NOT flat across the audio spectrum), the best strategy -- certainly the one I employ at home -- is to simply have sufficient copper between amp and speaker to prevent the speaker cable from causing trouble.
There are also quality differences in manufacture which have an impact upon things like long-term product stability. Use of poor grades of PVC in insulation, for example, will catalyze corrosion in the copper, and we see this all the time in Chinese products (usually of no known provenance other than "Made in China").
That's more or less the state of things where speaker cable is concerned. Interconnects of various sorts have their own particular quality considerations which vary depending upon the demands placed upon them -- since those are high-impedance circuits the sheer amount of copper becomes less relevant, while things like impedance stability (in high-bandwidth cable like SDI or Cat 6) or capacitance and noise rejection (in analog audio) become more relevant.
Kurt
BJC