I thought I remembered someone posting here in these threads that the PS2 version ended up outselling the GC one even in the US but I can't find that post. Apparently it's wrong anyway but world wide sales favored the PS2 version.
Sorry, I hadn't seen your reply until now. Apparently what I said about SC2 in the US was wrong. Yet looking at WW sales Namco's decision still makes sense.
Wasn't Soul Calibur 2 re-released in that PS2 collection package with Tekken 4 and Tekken Tag, though? That must have sold something... who knows if it was enough though.
And I notice that you argue that Namco made decisions based just on the Japanese market when Western sales would dictate different decisions. But in reality those better Western sales are better American sales as Europe was more in line with Japan. So Namco is actually not doing what you think they are, making decisions based on just one market.
The world wide sales numbers are what should matter most, and thanks to those good US sales, Symphonia and Soul Calibur II sold quite well on the Gamecube. That's the point. Sure, those sales were more in one region than the others, but the worldwide total is what matters most...
As for ports, in today's two HD console climate we are puzzled by the lack of more multi versions in the gens before but at the time it was the exception not the rule. In most cases publishers like Capcom or Namco who decided to give the GC a chance ported their stuff to PS2 to not lose sales. So they ported to the more successful console to maximize sales, not to less successful ones even though it would have meant some extra sales
Well, as I said there's lots of variability here -- Western third-party games which are exclusives to a single platform, and Japanese games on many systems -- but as a general trend, I think it is pretty clear that Japanese publishers are less likely to do ports of games on multiple systems, and it goes back to well before the big Western shift over to consoles in the '00s. That probably did make the difference more obvious, though, for sure...
For Japan in specific though, the issue often seems to be focusing just on what sells in their home market, and not what'll sell anywhere else. That is a mistake, when their market is not as big as Western ones, and is a shrinking part of the global total.