I've thought about this off and on for a while, and this comment reminded me.

His last video was released in October of 2004, and statements made in the tape seemed to indicate that the tape was at least as current as late summer of that year. Since then, nothing on video.

It seems incredibly unlikely that there wouldn't be some attempt to at least get a photo, much less a video. We already know that their organization has ways of getting audio tape out through networks of couriers. An 8 mm video tape isn't any bigger than an audio tape.

I've heard that the audio tapes have been "authenticated." How certain is that?

It seems very likely that if bin Laden did die, his people would keep it a deep, dark secret for obvious reasons.

I can think of a couple of other reasons why a living bin Laden would not have issued a video in two years, but they seem more unlikely than the most obvious reason.