Like you said, to forge an original well enough to pass expert scrutiny is very difficult. However, some of the things you listed, such as the paper and watermarks, can be circumvented somewhat by running it through a copying machine a few times. Based on that PDF file, it appears they did this and/or sent it via fax to make the document harder to examine and to appear old.

It's the little things that can trip you up. I read a news story last year about a spy museum that opened in Russia. One of the tidbits revealed why American spies traveling with false papers were picked up so quickly in the Soviet Union. It was the staples. The Soviets used steel staples that would rust. American staples didn't rust. The Soviet security officials could immediately pick out the false documents by looking at the staples.

Whoever it was that tried to pull off this almost certain forgery was an amateur. They counted on a gullible (biased) news media that would fall for it, and they were right. They didn't count on thousands of bloggers raising the bullshit flag enough to get verification experts to look into it. CBS was busted, and I hope some high profile heads will roll over this. Their credibility is damned near zero, and without credibility, they won't long exist as a news outlet.