I don't know why people are so surprised that the metagame is becoming more and more centralized (at least decreasing in variation). While the game has a fair level of complexity, the information contained in the game is limited while time is essentially unlimited. Therefore, over time, people will only refine strategy within the rules of the game. By "refine," I mean that more effective pokemon and sets will be discovered, and weaker ones removed.
Left to its own means without outside stimulus (changing the dimensions of the game via rule changes or new pokemon games), it's natural that the metagame will become more stagnant. It happens slowly, with this or that player shaking things up once in a while, but generally speaking, looking at the bulk of play, the trend is towards conformity. That's just natural.