It may be the case that identity is part of any contract dealing with property by logical necessity (since property cannot exist but with the identity of the proprietor - you can't go to the bank and ask for your money if you refuse to identify who you are even if it is in fact your money).
This is surely not the case. GLBSE did not know the identity of the users, so this information cannot be used for authenticating the request against gigamining.
The bank also only needs this information because you proved your identity to them when you were opening an account in the first place, and there also used to be bearer-instruments. Due to stupid laws, these have been to a large extent eliminated, but when I was younger, there were bearer passbooks.
Most transactions are conducted using Debit/Credit Cards and you prove ownership not by providing ID but by providing knowledge of a secret (the PIN number).
Similarly the exchange with which MPOE-PR is associated (MPEX) allows withdrawals and transaction without providing ID - but by proving knowledge of a secret (a private key).
To an equal extent ownership of an email and/or BTC address can be proven without providing ID.
In this case no ID was provided (or requested) when entering the arrangement - so proving ID NOW doesn't get anywhere nearer proving you controlled that email address/BTC address at the time at which the agreement was entered into.
To be clear: If you believe nefario's list then you don't need the ID to prove ownership. If the list is treated as unreliable (i.e. the existence of an email/BTC address on there isn't itself accepted as proof of ownership by whoever controls them) then providing ID doesn't prove OR disprove ownership.
That's why I'd conclude the request has nothing to do with proving ownership - and everything to do with trying to cover his arse: the costs of which (to investors as well as to him) are his responsibility as (in short) he's the one who chose not to do it in the first place and the one who had the responsibility to disclose the need for it if it was required of him by regulation/law to obtain it.