He specifically addressed this. He stated that setting a precendent for proof-of-life via a PGP message is bad and they wanted to avoid doing it. It's bad becau

He specifically addressed this. He stated that setting a precendent for proof-of-life via a PGP message is bad and they wanted to avoid doing it. It's bad because it doesn't actually prove anything. He said it is hard to secure PGP keys, and under extreme pressure Wikileaks may lose some. Really if you don't believe he's alive for the reasons I posted above, it's likely that nothing will convince you!