Maybe I've completely misunderstood how blockchain works: but I understood there wasn't really anything in a bitcoin 'wallet' apart from a public key and a private key. You know how much you've got because you basically total up your entries from the entire ledger from block 0 to the present day. When you make a transaction, you tell lots of people and eventually that gets imortalised in a tamperproof block (by miners?) which, once created, is also shared with lots of people. If you are 'keeping your bitcoin' in some place X, surely that just means you've stored your private key there?