In the original games you could catch either of the eon pokemon (depending on version) if you got some ticket...if I remember correctly you had to recive the thing from a friend
I am also jelly that SPOILERS: in the post game of ORAS you can catch Deoxys who was originally an event pokemon and who is one of my favorite legendaries. like its my childhood dream come true ^^. Thats the same like if the Sinnoh remakes let you get Darkrai or something .
Have you seen the number of legendary Pokemon you can catch in the post game? It is ridiculous. I now have Mega Rayquazza. I am going to space soon to get your favorite! ^_^
I'll never catch them all. I still have Battle Maison to check out too. So much adventure!