I think Wright is just a smooth-talking conman with some crypto experience. I'm betting he met Gavin and other (unfortunately, merely "supposed" at this point...) experts in person, talked shop for a while, then took out his laptop and staged verifying the signature of blocks 1 and 9 with dummy commands. (Edit: Gavin actually claimed it was a clean computer, not one that Wright brought. Disregard that.)
The Economist actually states this directly:
>Mr Wright has also demonstrated this verification in person to The Economist—and not just for block 9, but block 1. Such demonstrations can be stage-managed; and information that allows us to go through the verification process independently was provided too late for us to do so fully. Still, as far as we can tell he indeed seems to be in possession of the keys, at least for block 9. This assessment is shared by two bitcoin insiders who have sat through the same demonstration: Jon Matonis, a bitcoin consultant and former director of the Bitcoin Foundation, and Gavin Andresen, Mr Nakamoto’s successor as the lead developer of the cryptocurrency’s software (he has since passed on the baton, but is still contributing to the code).
Relevant bit:
>Such demonstrations can be stage-managed; and information that allows us to go through the verification process independently was provided too late for us to do so fully.
For Gavin's demonstration, he claims Wright validated the signatures on a "clean" computer, with the implication that it could not be staged.
>Part of that time was spent on a careful cryptographic verification of messages signed with keys that only Satoshi should possess. But even before I witnessed the keys signed and then verified on a clean computer that could not have been tampered with, I was reasonably certain I was sitting next to the Father of Bitcoin.
So, either the clean computer wasn't really clean, or Gavin's complicit in the scam, or Wright does have Satoshi's private keys and may be Satoshi.
Either way, why would Satoshi want to prove it yet only demonstrate proof to a few people in private rather than putting a message and signature online for anyone to verify?