I don't know anyone who buys both versions (red & blue, gold & silver, etc). My sister and I used to get opposite versions -- it was fun. It was like we were both playing almost the same game, but the little differences changed the experience. It made it more fun to talk about.
GameFreak doesn't care about people buying both versions -- that's certainly not their intention. From the start, the purpose of dual releases has been to encourage discussion and trading between friends. Not to "trick" people into buying two games at once. Some people do anyway, and they may be a bit fanatical -- or maybe they just want to start a new save file without erasing their old one.
By no means do I hate Call of Duty, but come on now. Don't compare COD to a game with dozens of hours of single-player content, near-endless customization options and replayability, loads of post-game content, and a thriving competitive community to boot. A well-behaved competitive community.
