As someone who is quite ignorant on this topic, did anyone reading this check the signature he used (or know how to)? If he did fake it, why would he do that?
Why? Maybe for fame & assoc. income. Tho Satoshi has access to many BTC. Real SN wouldn't need more. More interesting, how he thought could get away with. Does he know who real SN was?
Basically if you don't trust Gavin's word on it it's impossible to know. What convinces me is that there's a sustained smear campaign that has the hallmarks of a banker hit job.