That is an incorrect or incomplete representation. The doctrine is published by the Church and merely resides in the Standard Works et. al. You cannot open any of the Stadard Works and point to verses and tell someone else what the doctrine is in most cases without referring to some other work published by the Church. For example, you do not know that the water in John 3:5 means water baptism as opposed to the evangelical interpretation of physical birth. Another example is the doctrine that those who do not have opportunity to marry in this life will have such an opportunity in the next. Or abortion being like unto murder. Etc.
The upshot is that it takes modern prophets and apostles to establish the doctrine out of the scriptures as well as continuing revelation (which is rarely canonized). It is then officially published in a manual, or magazine, and yes, even artwork, al of which the Church lists of sources for us to use in teaching the doctrine, keeping it pure, and as the voice of the Church.
A scripture only view does nothing but deny the prophets and apostles and the need thereof and is in complete opposition to how the Church sees it's own doctrine.
Elder Christofferson's recent GC talk is an excellent illustration of this even though it concentrated more on the establishment side than the publication side (though he did give an example of such).
Not being published by the Church, one can indeed safely ignore the JoD or BRM's "Mormon Doctrine" etc. However, items from those are often found in works published by the Church and those items are therefore official doctrine because of that.
There's another ongoing thread that discusses how the Word of Wisdom was at first essentially a "suggestion" but under Grant (if I recall correctly!?) it became doctrine. If that development proves accurate, it would seemingly prove an example of "doctrine" found not in the standard works.
The JoD has always proven an interesting discussion point for me. At some point in the near future I'll throw a new thread out there so I can get some wider feedback from the forum members. I know LDS folks who never look at them (either because they don't seem super relevant to their personal growth in this age or because they essentially have suspect publication origins as described above), whereas others throw themselves into detailed study of the Journal (Journals, plural is more correct?).