The explanation to me was that because folk make reduce the output and then amp it later which could produce hiss Samsung decided to go with fixed level output. Of course this means they fixed one issue only to create another complaint.
I am amazed that my Samsung TV does not allow control of the audio level when using an external amp. It would have been so simple to make that happen. If you hook up an external amp via the rear 3.5mm jack you will find that the Samsung remote will not control the audio level on this output. So make sure you get an external amp with an IR remote. Yes - yet another remote to lose!
I really can't think of any reason why Samsung designed it this way. (and yes - I am an electronics engineer!)