Google "squinting modifiers" or "two way modifiers". Essentially, it's all about writing in such a way that you can't be sure if a sentence means one thing or another thing. WT is great at that! JW's are vague because the literature is often vague. There are many such techniques designed for "wiggle room" instead of clarity. Quite useful when doctrine changes or elders want to "beat" a publisher into submission, eh?
Is it done purposefully? At one time I would have thought "no", but then I read something Barb Anderson wrote concerning the magazine article "Women Deserving of Respect". Does it mean that all women deserve respect or that *certain* women deserve respect? Apparently there was quite a bit of dissent around publishing the material at all. The result was an ambiguous title and vague material. The Writing Department knew all along that they weren't presenting a clear message.