To answer pitflyer's comment, I am attaching the following, received from Marriott in response to my letter. I think this confirms that the promotion is targeted to Silver members only. It does not confirm that ALL Silver members are eligible, but it definitely comfirms that NO Gold or Platinum are eligible.

Dear XXX,

The "Silver Elite Double Points" promotion is a promotion sent out by our Corporate offices. I apologize that our office has been advised that no Platinum or Gold members are eligible for this promotion. Corporate is trying to get our least frequent stayers to make more stays with this promotion.

We will have future promotions that benefit you, our most loyal members.

We appreciate your continued loyalty to Marriott and look forward to serving you again soon.

Sincerely,

Niki Hovanes
Marriott Rewards