I do not know about the New World Translation but I do know that if you apply that bishop's application of what I like to call the Bible copyright to all of scripture, then we would all need to throw out Christ and pretty much everything after Deuteronomy as it says pretty much the same thing. In Deuteronomy 4:2 and 12:32.
Those passages are not saying that God will never give us new revelation. If that was the case then everything after Deuteronomy chapter 4 should be dismissed as a lie and thrown out. But that is not the case. Those passages are directed towards mankind not God. Scripture is basically a record of God's dealings with mankind. The Bible was likely compiled by prophets of God from a larger source of records which are now lost to the world. From there it was recompiled by a group of theologians who decided of themselves what was and was not scripture.
The Book of Mormon was compiled from records kept over more than a thousand years by a prophet of God and delivered to another man called as a prophet who then translated it not by his own power or wisdom but by the power and wisdom of God.
The Bible is rightly held up as the world's greatest treasure. It is the only record that we currently have of the earthly ministry of Christ. However the Bible is not complete and anyone who says that it is complete, is calling God a liar and are ignoring the promises that God made to the Children of Israel recorded in the Old Testament.
The Bible as we have it today is really a record of God's Dealings with the ancient Jews, one of 12 tribes or parts of God's ancient covenant people. The remaining 11 tribes are touched on but for the most part excluded from our current Bible. There are prophecies about the gathering of Israel as a requirement prior to the Lord's second coming within the text of the Bible mostly the Old Testament but the Bible none the less.
The Book of Mormon is a record of one of those remaining 11 tribes or parts of God's covenant people and their dealings with God.
So really the Bible is part 1 of 12 when you factor in all of the branches of God's Chosen people.
Thus the question of the Book of Mormon is not should it have been written but is it actual scripture inspired by God.
Here is a list of scriptures that talk about the scattering and gathering of Israel
http://www.lds.org/scriptures/gs/israel/the-gathering-of-israel?lang=eng
Here is a list of scriptures dealing with the gathering of Israel.
http://www.lds.org/scriptures/tg/israel-gathering-of?lang=eng&letter=i
Both of those lists have scriptures from the Bible and from scripture used exclusively by the Church of Jesus Christ of Latter-day Saints.
If you have any questions please feel free to email me and I will be happy to try to answer them.