The Armenians changed the date?
In Jerusalem they celebrate Easter on the traditional date. Elsewhere it's been changed to the Western date. I think the change was done after the Genocide to accommodate all the Armenians who were living in diaspora in Western lands.
No... Not everything has to do with the Genocide.
In 1923, there was a movement in ecumenical circles to get all of Christendom to celebrate Easter on the same date. The Armenian Church changed the date at that point in time. Jerusalem maintains the old date because of the Status Quo and the special position the Armenians hold within the Easter celebrations in the Holy Land (the Holy Fire, etc.).