Nintendo 3DS and Wii U have both ushered in the potential for Nintendo to add paid DLC options to games, and it's already happened with titles like Fire Emblem: Awakening and others. One thing we haven't seen, however, is the ability to buy Pokémon in games such as the recently released Pokémon X and Pokémon Y, and there's a good reason for that.
While speaking to 4Gamer, as translated by Siliconera, Pokémon art director Ken Sugimori and director Tetsuya Watanabe spoke about why we haven't been able to purchase Pokémon with real money in any way. According to Sugimori, saying "no!" to this is something that traces back to the days that series creator Satoshi Tajiri was heavily involved.
Sugimori sees paid DLC as "one of the things that could 'ruin the worldview' of Pokémon."
"I believe the reason we don't simply commercialize [Pokémon]," he says, "is that it's a way of protecting the brand, and for this purpose, we have the specialty company called The Pokémon Company. Therefore, suppose we sell a Pokémon for 100 yen, then we must prepare something that is worthy of that 100 yen, along with a reasonable consent for doing so."
Sugimori goes on to explain why they're able to give away legendary Pokémon to fans who see the movies in theaters, and other ways they endeavor to remain consistent with the franchise. Definitely have a look at the full article. While their stance on paid DLC is admirable, you'll find it isn't entirely out the window just yet.