The assumption that cable manufacturers promote longer speaker wire lengths to increase sales is an easy one to make.
If you use short speaker wire, you need long interconnects. Right? Has anyone researched the total cost difference between long IC with short speaker wire vs. short IC and long speaker wire across several makers' products?
I sampled pricing from Harmonic Technology and Audience just as a starting point. The pricing is only a bit higher with longer speaker wire.
A 3m pair of non-biwire Audience Au24 SW is $93 more than a 3m pair of Au24 IC (RCA). Not enough to support the profit motive theory.
In the case of HT, there is more material in their speaker wire than in their IC; so, manufacturing costs may be higher for SW (speaker wire) and thereby justify the marginally higher cost per meter.