"At this point, we're not thinking of going in that direction. Trading is a core concept of Pokémon. So when you're trading, you meet with a friend and decide which one you want and which one they want. I would like to emphasize real-world communication. You don't see each other online."
Honestly that is the worst reason for it. Seriously, especially now that they've added wifi capabilities to DP, that doesn't even make sense. If they had an MMO then there WOULD be communication. If you wanted to trade or battle, you'd have to go up to a trainer and engage them. None of this impersonal friend code and arranging trades on an unofficial forum, etc. They're just scared of having to moderate communication to keep the kiddy feel to Pokémon which sucks. :( I wish they'd at least come right out and say that instead of giving crappy excuses like they just did.