I actually think that some legendary pokemon can be caught. Some of these include Heatran, which in a way, was caught in the movie. If there was a pokeball at that time, that guy (what his name?) would've caught him. The four swords of justice can be be caught too, as they don't really have power over the world. Plus, I think Cresselia and Darkrai could've been caught. It could've spiced up the storyline of the anime. Especially the fact that he had a large impact on the Diamond and Pearl anime.