Coming from a Kotaku interview with Pokemon Co. head honcho Tsunekazu Ishihara...

"Until now, the pattern has been to release games overseas a few months after the games have come out in Japan. By releasing [Pokemon X and Y] simultaneously and allowing players around the world to enjoy the game on an equal stage, even I can't fully anticipate the outcome, and I'm looking forward to seeing the results. I believe that Pokemon has always been 'a tool to connect people,' so it's interesting to see how playing the game evolves in areas – including the release timing – and how word spreads through the media comparatively."

When asked about sales goals for X/Y, Ishihara stated that they're looking for the game to hit 'Diamond and Pearl numbers', which amounts to over 5 million copies in Japan.