I don't know why you would need to activate them all on the same day (and in fact that did neither happen in the US nor anywhere in Europe). An incremental rollout is always possible and the size of a market does not change anything about that. My European credit card still works with legacy systems deployed somewhere in the world that hadn't been updated. That doesn't change the benefits they got from updating most system here.

Incidentally, the large schemes usually set Europe-wide rules anyway.