If windows decided to cut your file while bitcoin was running, then you are screwed because bitcoin could not save its private keys before backup.
Is this really the default behavior of the QT client? Because that would make it very susceptible to something like a power outage or computer crash. I would imagine that any newly generated private keys would be immediately stored in the wallet file (in addition to being kept in RAM).
Private keys are pulled out of a "keypool". Once the keypool runs out, it is refilled. Therefore during a power outage, unless a new keypool was generated, you will still have all your keys.
What I don't understand is that I sent a transaction to an address generated in QT--and the transaction showed up. I clicked and dragged the file to my desktop and them immediately to an external drive. I still have the file--but when I put it back into the bitcoin folder (C:\Users\ken\Appdata\Roaming\Bitcoin)--the account shows 0 coins
In addition to private keys, wallet.dat also keeps track of your transactions. If you moved it before bitcoin could write transaction details, the copied wallet.dat will not contain the transaction. However, bitcoin generates a "keypool" when the wallet is first created. If those keys were successfully saved, you can probably recover your coins.
So what I don't is that somewhere there is a BTC address with the money assigned to that address/account, and I have the address. So why can't someone, somehow claim it? Where does it go? It is 4 coins which were lost--so is someone else going to be able to take it?
The other thing I don't quite understand conceptually is what a private key has to do with it, where to find it, and even how to use it to recover the coins if/when I get the key. Perhaps when I digest the page you sent me to that will become clearer--but I have such a headache now I will have to try later.
That's how cryptocurrencies work. The only way to claim possession is through the private key. No key = no cash.