The short answer is that some church leaders and others have commented on this subject, with various points of view taken.
In addition to B.H. Roberts, there are also some leaders and scholars who have stated that Joseph FSmith's use the language of the KJV was a choice, while remaining somewhat more agnostic about the exact process behind how that wording was put in the translation. SmithFor instance, LDS scholar Hugh Nibley appears to also adhere to this view, which he outlined his thoughts on this in response to a letter to the editor of the Church News in 1961 (reprinted in The Prophetic Book of Mormon, ed. John W. Welch, volume 8):
As to the "passages lifted bodily from the King James Version," we first ask, "How else does one quote scripture if not bodily?" And why should anyone quoting the Bible to American readers of 1830 not follow the only version of the Bible known to them? Actually the Bible passages quoted in the Book of Mormon often differ from the King James Version, but where the latter is correct there is every reason why it should be followed... Since the Book of Mormon is a translation, "with all its faults," into English for English-speaking people whose fathers for generations had known no other scriptures but the standard English Bible, it would be both pointless and confusing to present the scriptures to them in any other form, so far as their teachings were correct.
In addition, in the 1966 edition of Mormon Doctrine (p. 302, entry titled "King James Version of the Bible", electronic copy here), Bruce R. McConkie appears to take this stance:
Joseph Smith read, respected, reverenced, and taught the King James Version "as far as it is translated correctly." (Eighth Article of Faith.) Whenever he found Biblical quotations in the Book of Mormon (they having been copied from the brass plates and preserved by the Nephite prophets), he rendered them into English in the exact language of the King James Version, except in instances in which the language of that version did not convey accurately the original thought.