I also think a lot of the fun is in battling someone that's sitting right next to you. Is Pokemon's target audience really going to enjoy battling some random person hundreds of miles away as they would someone next to them, that they can communicate with, mock and enjoy the resulting bragging rights with? I think the same goes for a lot of other games people really want to go online, like SSB. Playing alone in a room with some other human players somewhere else in the world might be better than nothing, but it's not better than playing with a couple buddies that are sitting on the same couch. So... I think a significant appeal of the portable nature of the main Pokemon series is that the gameplay is complemented by the real life interaction that occurs around it.