No one has really given you the "official" explanation. While I do not support or even like the change, I will explain what Lucasfilm has come out to say about it.
Anakin's "real death" was when he became Darth Vader, not when he was redeemed on the DS2. When his ghost appears through the Force at the end of ROTJ, its showing him as he was when he had his "real death."