I3LuEI3omI3eR on 29 September 2014
You answered it yourself, it's to buy both versions of the game, and if you like the game so much you'd buy 2 of the same version just to keep your saved file.
Trust me I used to go to Nintendo World lots and there were some kids who has like 2 Blacks and 1 White. It wasn't common, but it wasn't rare either. Big reason why Pokémon games sell over 5+ mill.
