Woa, settle down! It is prbably because of all the new moves. If you sent a pokemon with a new move back then it would mess up that game or something, and they cant just not let you trade them because almost every pokemon has a new move of some sort.
It isnt known how to get the old ones yet but there are pokedex entries and pictures unique to Ruby/Sapphire so there will be a way, for no just stick to training the ones in the game.
One can't complain. I have my friends. Someone spoke to me only yesterday.
Re: Why in the hell?
well how come the second series could trade with the first series? R/B/Y could trade with G/S/C only rule was that it couldn't be any of the new pokemon, and the pokemon couldn't have any of the enw moves.
Re: Why in the hell?
u can get the old pokemon by trading with leaf green and fire red or u can trade the pokemon from leaf green and fire red to emerald and get them frome emerald