Kojiro, havent a few pokemon learned some moves that they dont learn in the games. Im not sure but its just a hunch correct me if im wrong. Theres also the fact that the anime does tend to be different from the games.
Ash6K, im guessing that torkoal,corphish, and swellow will go to oaks. Swellow has had plenty of glory and has proved time after time of its awesomness. Torkoal just had a good battle and did redeem its poor performance through out the hoenn region. Gravy made a good point about corphish not really having a great battle that would be remembered. But i like to think of Corphish wiping out half of masamunes team, taking out a crawdaunt in the dragonaire episode, beating tuckers arcanine, beating anabels alakazam and then beating a pinsir and marowak. With that in my mind i feel like it perfectly fine for corphish to go.
O and ur question regarding bulbasaur. Many will argue that sceptile is stronger or bulbasaur is stronger. But the fact is that bulbasaur hasnt battle since the JOHTO LEAGUE while sceptile has had battles as a treeko to sceptile. It had a huge glory in the spenser battle, it took out 2 of his pokemon and learned solar beam. I've said it before and i'll say it again sceptile made an overused attack like solar beam look good again. There prob doing it cuz bulbasaur hasnt been used for such a long time and for the fanservice. And ofcouse as Geodude mentioned its only natural for ash to rely on his kanto trio pokemon in his hardest batttle who he may feel are the best choice against brandon.