Actually someone theorized it might actually have to do with the Pokeball itself, even if they swapped balls, Aipom would still belong to Ash and Buizel would still be Dawns so they had to use the machine so they actually belong to the right trainer. The person's theory was more complex but I don't think you want to hear it.
Originally Posted by Kataphrut
Also this may just be my theory but if it wasn't Ash or Dawn, chances are the machine makes it so a Pokemon will listen to the new trainer. I don't think swapping balls is going to cut it in that case.
Misinterpreting my posts is not your fault, negative repping me, and getting very sensitive about my posts because you misinterpreted my posts however is your fault. Think really hard, before negative repping or making a big deal about my posts. I don't appreciate being negative repped for reasons that are a result of misinterpreting my posts.