I remember that it activated the HgSs event but iirc you traded it from Pt to do so...
Both movies came at the end of their Generation though. After Deoxys' Movie was the Lucario Movie. After Arceus' movie is Zorua's.
Technically Gen 4 ended earlier than Arceus' revealing as Platinum came before HG/SS. Even though the remake is in Generation 4 its of a Generation 2 game, while Generation 3's remakes came between the main titles and the director's cut so you can't even use that as a comparison. Switch the places of the games and they come out to pretty much the same thing.
Serebii and Bulbapedia have conflicting Event information so I don't know which source to use, but Serebii has Deoxys Event data that predates Pokemon Emerald's release in Japan.
Arceus's event was started in July and ended with the movie in September. I mean both Generations ended as soon as the last Event Pokemon's Movie finished. B/W breaks all normal ideas so while there is still the chance that all the previous info is false, we can't use Event release as a reason cause if we do, then as most others say, Gen 5 has ended when Genesect was released. I say was, cause its already out in Japan just waiting on its movie.
Best Wishes is almost over too apparently and no Anime tie ins have been made yet like Lyra was during the Sinnoh travels. So we aren't getting very positive Anime assistance.