I have seen quite a few of these bogus "letters" -- supposedly written by Robin Williams ("The US will apologize to the world for our interference in their affairs, past and present. You know, Hitler, Mussolini, and the rest of those good old boys."), Andy Rooney ("I am sick of Political Correctness and all the suck ups that go along with it."), George Carlin ("I don't hate the rich. I don't pity the poor."), and many others: Paul Harvey, Dennis Miller, Jay leno - along with military leaders.
They're all of a conservative bent, and they're all supposedly given more gravitas because of the unexpected author. Its no coincidence that the only ones who actually believe them are the sort of people who think the fox network is a legitimate news source.