No he hasn't. This "memo" was published in an Italian newspaper. It has not been released publicly by the Vatican; we don't even know for certain if Ratzinger is the author of it.
If he chose to speak publicly and release this document publicly as head of the Congregation for the Faith, then it might influence the American bishops.
As it is, the bishops have voted to allow individual bishops to make their own decisions about refusal of the Eucharist.
In case you haven't noticed, what the bishops think has become largely irrelevant. 40 years ago, what someone like Cardinal Spellman said could have an impact, but that power is gone. Do you think it matters what any of those bishops say? Do bishops have any duty to instruct their flock?
Sinky advises CM55 that 'we don't know for sure who wrote this memo...' and further advises that the Cardinal did not "order" that Kerry be denied Communion.
There are countervailing opinions, and Sinky well knows it.
One can weigh the authorship issue this way: Cdl. Ratzinger, back in early June, said "X" Cardinal McCarrick, a world-class political slimeball, then says that Ratzinger said "Y."
This is literally a life-and-death matter.
Cdl Ratzinger is not a happy camper about the lie told for US Catholics' consumption. Now what does he do?
One thing that is RARELY done is a direct face-to-face contradiction. That's just not the way to do it. So Ratzinger or one of his aides slips the memo to the press.
Not surprisingly, it's to the ITALIAN press--they can be trusted, unlike the US papers, to keep the source secret (remember in the USA, the Press hates the Church more than they hate GWBush.)
Ratzinger has allowed the Press to call McCarrick a liar.
Another way to look at this: Cui Bono? (Who benefits?)
Ratzinger is defending some pretty significant core concepts here: the sacredness of the Eucharist AND the question of promoting abortion. Releasing the memo is for the benefit of orthodox Catholics--not for Ratzinger, who doesn't live or vote here---not for Bush (for the same reason)--and certainly not for McCarrick who is now obviously a liar and a hypocrite.
Only the Truth benefits--thus we can be even more certain in our belief that it is INDEED a genuine document.
As to Part Two of your query: You can see that the document does NOT name Kerry (nor David Obey of Wisconsin, nor Schwarzenegger, nor Giuliani, nor Kennedy...)
So no, R. did NOT order that Kerry be stiffed.