SILENCE IS GOLDEN: It has been one insanely busy summer weddingwise for Vera Wang — too bad she can’t talk about it. In the past two weeks alone, the designer has dressed Chelsea Clinton, Alicia Keys and Hilary Duff for their respective walks down the aisle. Mention of Wang’s name seemed to go hand in hand with the media’s coverage of the former first daughter’s July 31 big day in Rhinebeck, N.Y. But abiding by Hillary and Bill Clinton’s cry for privacy, the designer has yet to speak of her involvement. And as of Monday she wasn’t dishing about the airy confection Duff wore Saturday for a sunset Santa Barbara ceremony either. But while Duff may only be 22, she is old enough to know there is money to be had — before marrying Mike Comrie, she lined up an exclusive with OK magazine.