To be honest, I'm a little embarrassed by what I learned about the fact that the file wallet.dat is not completely encrypted. Now when you said this - i ask myself the same question. In fact, it's not so difficult, Why did not the developers do this?
Did you even read the thread? A lot of answers have been posted here.
The most obvious answer is, that it is not necessary to completely encrypt the wallet file.
Why should one need to decrypt his wallet (and expose it to theft) just to check his balance? Or just to copy a receive-address ? This wouldn't make any sense.
Therefore, the important (secret) information are encrypted, and the non-secret information are not encrypted. Thats the best approach regarding security/convenience.
