At its core, a wallet is just a collection of private keys. So yes, these are easy to extract and, in the original client, there is a simple command to do just

At its core, a wallet is just a collection of private keys. So yes, these are easy to extract and, in the original client, there is a simple command to do just that. Or, as mentioned, you can access the BerkleyDB wallet.dat file directly. The "bitcoin" itself is never really stored anywhere in terms of state-- the chain simply stores the series of transactions between public keys up to right now and you calculate the btc state from that. The wallet.dat also typically stores cached transaction data, but it's only a local cache and not authoritative.