The prosecution is alleging that the document leak perpetrated by Bradley Manning directly aided the enemy (al-Qaeda) in their operations against the United States. So what's the problem with including testimony that documents leaked by Bradley Manning were present during the Bin-Laden raid? It's common sense.
It is common sense that information in the PUBLIC DOMAIN is available to well everyone, including "the enemy". Calling the witness to state that Bin Laden seeeked public domain knowledge is just tugging on strings of nationalist emotions. The goal is to smear Manning to Al-Qaeda/Bin Laden (evil, bad, them, enemy) and
Variables don't; constants aren't.