I think it went like this:
'American AlQaeda' threatens attacks to satisfy his delusions of grandeur. Have AlQaeda ever preceeded an attack on the US with a warning? A videotaped message to those who they want to kill? I can't remember any other instances of it. Seems out of pattern.
AQ operative gives the tape to ABC rather than a web-release because he's afraid he'll get tracked online and caught. He's probably still in the US, as his face has been plastered all over the web. Heck, I've seen his photo over at pre-ban on an FBI banner ad.
He is a known AQ suspect, so ABC treats the tape seriously. However, they see it, know that it will affirm the contention "the terrorists would prefer Kerry to win" and hold the tape. They never had any intention of releasing it. And only after Drudge found out, did they have to do something with it.
My guess is that the AQ operative believed ABC would release it immediately. He didn't count on the perception that it would actually help GWB in the election. ABC has reportedly had this tape for quite a while (months?). The operative sees it has not been released, now knows why. We probably won't hear anything like this from him again.