Anyone can claim , but only one in each case can prove it . That's the point we are now , proving in court . Either he is or he goes to jail for perjury and other things . Isn't that great ?
Do you really believe he is Satoshi? Let's leave the court asides for a moment. Do you find the overall "evidence" convincing to you?
If i steal your keys am i the owner of your coins ? Or am i a thief who illegally posses your coins ? And more importantly , if i steal your keys am i you ?
No, but if you claim to be me, and you have other ways to prove such a thing (like a drivers license), then a signed message from the PGP is at least required. You can't claim to be an anonymous person with no evidence apart from forgeries. Satoshi, whoever he is, posted a PGP key. This, along with the genesis public key, are the only elements which can certify his identity. Beyond that, not much else is known about him.
You can't treat potentially everyone as Satoshi. Everyone is not Satoshi until proven otherwise. And as time goes by, these signed messages will count even less as solid evidence due to the development of quantum computing which will sooner or later be used to compromise his keys.