Re:
No, it was the down tube that was beefed up.
I assume the design philosophy was to employ a softer seat tube to complement the tapered stays and give a more sophisticated rear end, better traction etc. However that might have left the overall balance too flexy at a time when they were trying to make their steel frames stiffer, as aluminium frames were so popular. So they strengthened the down tube from a 0.9-0.6-0.9 to a 1.0-0.7-1.0 to compensate.
Overall, the weight came out pretty much the same as the Cinder Cone, but it was a better frame.
Marketing-wise, I suppose your assumption was pretty apposite. It may have been a better, and more expensive, frame so as to sit between the Cinder Cone and the Kilauea in the range, but as they didn't publicise the differences very well, many potential customers may well have assumed there weren't any. But then again, marketing men are less interested in details than designers are - and after all it was a much nicer colour, and you have to get your priorities right.