You would essentially buy the same game, the story is identical the legendary is different and a couple of pokemon but you can get everything in trade so not worth the money buying the same game
it allways was like this exept on pokemon XD ( not done by gamefreak tought) and pokemon yellow , no idea why the hell they release 2/3 ( emerald and crystal and platinum ) games all the time instead of just one like it should be
comon with gts trading is simplified the fact that they keep retarded system and having version exclusives to force trading is idiotic