Well, while I agree anyone can play Pokemon, I disagree with you that it's all softcore gamers. The actual adventure is playable by even those with the smallest grasp of the gameplay formula to be sure. It's very easy. However...
The online metagame for Pokemon is an endless depth of strategy, and the best gamers are akin to worldwide chess champions in strategic ability. The game's formula isn't nearly as simple as most people think. I could right a 5 page paper on the intricacies of Pokemon and it's strategies. Most people think there is nothing more to it than this type beats that type, but what make Pokemon so successful is it's appeal to everyone, casual and core alike.
As far as popularity, Pokemon is the second best selling game franchise of all time, outselling Final Fantasy by a vast amount. It's undeniably the more popular franchise, both in Japan and worldwide.
