Lucario, Blissey, and Absol are simply the best bang for your buck (energy) pokemon released in the last 3 sets. Therefore people will try and exploit that as best as they can. Lucario benfited from a complete lack of any Psychic threat fast enough when the sets rotated, without that I'm not sure it would have had as much of a huge impact that it did. Blissey was so good that despite a heavy Fighting presence in the format it was still played, and so versatile that no less than 5 different decks based around it as the backbone are viable in a tournament setting. Absol is another good card that can be put into just about anything because of it's first attack. Imagine how much less play Absol would have if Baleful Wind needed :dark: rather than :colorless to disrupt the opponent.
Despite all that there are still many decks out there that don't use any of these cards. Empoleon, Electavire, Gardevoir/Gallade, Honchkrow, K2, Magmortar, Hurrincane, R-Gon, Inferacatty, and Monarchy can all easily get by without using any of those 3 cards above.