This is the Japanese gamer market we're talking about here. You really can't be surprised when some 8 year old cartoonish creature collecting game like Pokemon sells better than, well, just about anything else over there. As much as the western market is full of gamers that just suck up, swallow, and breathe just about anything gaming-related that comes from the island nation, the simple fact is that Japanese gamers' tastes in general tend to be far more eccentric than what most westerners could stomach over an extended period of time.
In short: color me not surprised.