Why does the standard Bitcoin client not display the balance per address? Any Bitcoin wallet holds several bitcoin addresses. Such addresses are either generated manually from the GUI addressbook or automatically collecting the "change" of a "Send" transaction. The total balance is the sum of the credit of all addresses.

Why does the Bitcoin software not tell me ADDRESS1 holds 1 BTC while ADDRESS2 has 5BTC? 

The standard Bitcoin client automatically selects an address to send from. (From the comments, I learned that there exits a patch, which allows a user to choose an address to sent from.)

Does the behaviour of the standard client described here have any advantages over letting the user choose?
The balance of an address is almost always useless, since money is sent from random addresses.