Q:

Why don't these transactions add up to the account's total balance? 

I'm looking at the balance of this wallet address: https://etherscan.io/address/0x9a77d0900323b5f2b6cff6138569846406cf7456
There is an IN transaction from Poloniex to this wallet of ~33 ETH, then an OUT transaction to The DAO of ~33 ETH, then an IN transaction of 1 ETH.  Wouldn't the balance therefore be ~1 ETH?  Why does the balance on this account show as ~34 ETH? 
If the DAO was refunded to this wallet and that is why the balance is higher, where is this shown? 

A:

There is actually one more transaction you are missing, which can be found on the "internal transactions" tab:
https://etherscan.io/address/0x9a77d0900323b5f2b6cff6138569846406cf7456#internaltx
When you include this transaction, you will see that the books balance again. 
Internal transactions are those sent by a contract instead of directly from a Externally Owned Account ("EOA" for short).   Because they happen "a little further in" to the series of events triggered by some original action an EOA took, they take just a little more work to be identified, and not all block explorers show them.   To reflect this different status (as well as the fact that the internal transactions which will eventually result from a currently unconfirmed transaction can't be reliably predicted), Etherscan shows the transaction on a separate tab.   But the balances they transfer are regular ether, just like everything else!