This is the most intriguing headline/story I've seen in years.
What could possibly be in Bin Laden's porn collection that would justify or explain this decision. The most charitable is that they don't want to describe it because it's "moderately extreme" (eg paedophilia but not, for example, snuff movies) and they wouldn't be believed unless they released the material, which of course, would make them accomplices to sex crimes.
So they'd rather protect his privacy than have to defend their integrity. Interesting choice...