You're only wrong on this part. Both Jiranchi and Deoxys were released after Gen 3 for the other generation games. No Event Pokemon is exclusive to the generation they were originally made for. They carry over as wifi downloads in future games.
Deoxys was last released world wide for Gen 5 this year. May for those of us in the US and July for other countries like Spain and Germany....I actually think I missed this one D=
Jirachi was released world wide through Gamestop and Wifi for 4th Gen games in 2010. He got 5th Gen event release for Korea and Japan only.
Event Pokemon aren't exclusive to their home games and are only exclusive to event releases.
We may actually get a Gen 6 Jirachi if the Decora Arc that the Anime is going through doesn't end in the US before Gen 6 is out. If it does air, we can probably get a 5th Gen Jirachi before Gen 6 release.