AFAIK, the AIG he's talking about is a small (formerly) Swiss/international private bank (now owned by a company from Abu Dhabi). It's not the US insurance. (Google 'swiss AIG').
Copyright © 2003 - 2008, AIG Private Bank - A Member of American International Group, Inc.
Edit; It looks like it has been sold to an Abu Dhabi holding company, probably since the book was written, but it was formerly owned by AIG. I'm not sure why their website says they're still owned by AIG. Strangely, for a bank he claims has multiple billionaire clients, it was sold for only $254 million.
Not really. Chase has ~800 billion in deposits. You don't see it being valued at $800 billion. That is because every deposit is a liability just like how cash is an asset and most of the cash is loaned out which turns it into more assets. In a well run bank, these assets and liabilities cancel each-other out very closely (wrt banking reserve requirements etc...) and don't factor directly into the value of the bank.
As it so happens, CS people are much better at computers than economists etc... though there are some excellent econ. blogs on the internet which I enjoy reading.
Its a matter of specialization. I just happen to have banks as on of the things I try to specialize in.