Typically, the television show, trading card game and video games all release in Japan near simultaneously. Originally, that was not the case. The video game released first in February 1996 (JP), then the trading card game (October 1996) and television series (April 1997). It was not until recently that the video games began releasing world wide... I think it began with X & Y.
For those of you unaware, Wizards of the Coast (Hasbro), who owns Magic: The Gathering and the Transformers trading card games also originally published the Pokemon Trading Card Game. They were not really sticking to any series overarching story or video game tie-in, but they did introduce the new characters as they could. When Pokemon took over the trading card game in 2003, they started lining sets up with the television series and video game, beginning with Ruby & Sapphire (TCG: EX Ruby & Sapphire), although typically with a three or so month lag time.
Pokemon has been slowly lining everything up, so WPM's theory may be right on the nose. Magic: The Gathering releases in all languages worldwide simultaneously. Actually, I cannot think of another trading card game that does not release in all languages at the same time, short of Yu-Gi-Oh. The Pokemon Company International may simply be moving away from the Japanese model of distribution so that they can retain some uniformity. Something that is especially useful when it comes to championships where the American players are handicapped because the Japanese players have a set or two released ahead of them.