I would say that gamers are just being more cautious due to Final Fantasy XIII's reception and the fact that it's a direct sequel. Plus, Final Fantasy XIII had 3 years to build up hype and collect pre-orders.
When lots of Japanese commercials are shown and word spreads that it's a good game, I reckon it will sell 800,000 - 900,000, bearing in mind I know absolutely nothing about Japanese sales, just a guess. :P
EDIT: The guy below me copied my thing, only I'm allowed to guess rediculous accurate numbers.
823,162