Phantasy Star Nova certainly could have sold a lot more than 200k, if it was the game people wanted it to be. I think before details were made clear and the demos were released, most people speculating on sales based on limited information would agree that it could do well over 200k. Closer to 500k even.
But it wasn't the PS Portable successor people wanted. It was something else dressed up as that. tri-Ace did not make a game PS Portable fans wanted, so they didn't buy it. With all the free demos, people have enough chances to consider if they wanted it before it was released.
The same goes for SaGa here. The game could well be a dud. But if it is the proper SaGa game that fans have been waiting for, it can definitely sell over 200k. The audience hasn't just died overnight. It's not about nostalgia marketing. It is also about what the game itself is. I already discussed some of my concerns about how the game might be more disappointing than we expect in the current SaGa thread, and whether those fears turn out true or not will be cleared up when they show the actual game this Sunday.
