It really depends, dear IO (peace to you!). In a less formal/informal situation (for example, this forum or other situations where the author isn't really intending a bona fide publishing), it may not be normal or necessary since many don't understand the basics of plagerism, libel, and such... or are looking for indications of such. In these situtations, however, one really should be ready to PROVIDE their source if ever challenged to do so. One should also try to include things like quotation marks, when appropriate, so it is known that the thoughts/words aren't really his/her own.
In a formal setting (for example, a formally published essay, article, or book, a contracted/assigned or formal paper/report or, as stated above, always in academia, etc.)... it is not only normal or appropriate... but is expected and is supposed to be absolutely mandatory (have you noticed, that virtually every other "news" magazine or similar periodical prints retractions of errors that appear them... but NEVER do you see such in a WT/AW?. I digress...).
The WT is a formal publication. So why do they write the way they do? Many reasons, most of which were touched upon above, including, perhaps a lack of formal education in the Writing Department (though I'm not so sure). Most often, it is so that they can mislead and continue to push their false teachings, which they do by MISQUOTING sources... which they do left and right! One very good example of this is that for YEARS they quoted from the "McClintock's and Strong's Cyclopedia" (well, they still do since they often recycle information). Many may not know this, but this was a primary source of "Biblical information" for them.
http://en.wikipedia.org/wiki/McClintock_and_Strong's_Cyclopaedia
It is "the largest theological or Biblical encyclopedia ever undertaken by American editors" and has been considered as having "Thorough coverage of the entire field of Biblical and religious knowledge." Apparently, the old WTBTS leaders thought so... to a greater or lesser extent. Truth be told, it may be the very "tool" Russell and others used to get their little publishing company off the ground. Again, I digress.
Anyway, this was not a readily had source for the rank and file because, as all encyclopedia's used to be (during the Pre-Internet Era), they were VERY expensive. We (my husband, actually) just happen to have a full set, though (he found it in a used book store, for a "steal"). And in reviewing it (which we often do, me for amusement, because it was written in the 19th century) we've found two things:
First, the WTBTS often (and I mean often) seriously misquoted/misquotes the references contained in it; and, as I said, it was written in the 19th century and, therefore, its references are often... well, let's just say a whole lot of things "no longer apply" ("are archaic" would be entirely inaccurate as some of the information is quite accurate, appropriate and reliable).
Anyway, reading it is an eye opener: you can almost "see" the minds of the founders of the WTBTS churning away... as they contemplate establishing a publishing corporation... for which they would sell shares... using "true religion" as the draw and a great deal of info from the M&S Cyclopedia in the Prospectus. Anyone would have fallen for it, back then.
I hope this helps and, again, bid you peace!
A slave of Christ,
SA
