The page (and the quest itself) say that the ceremony will be downgraded if your partner doesn't buy the same plan that you do. And for the ceremony, that makes sense. After all, you can't really have the two players getting different ceremonies when they marry each other.

For the items on the other hand, neither of those is true. It makes no sense for one player's items to be based on what their partner did or didn't buy. Nor does the site indicate that it will happen. If somebody pays for the platinum wedding items, then they're entitled to actually receive those platinum wedding items that they paid money for.