I had heard, saw, or read somewhere that standing wood was the way to go. I guess the source was unreliable.
Perhaps just out of date. There are two issues here:
*) What makes the best fuel?
*) What is acceptable behavior, both individually and collectively?
Frankly, standing dead wood and the dead branches of trees make the best fuel. They will probably be dry and not rotten. Push over one dead snag, cut it up and split it, and your fuel needs are taken care of. Break of some dead dry lower branches and you'll have a nice cheery fire going in no time. "Dead and down" may well be the poorest quality fuel, because it is apt to be damp and/or rotten.
The more important thing to consider, however, is acceptable behavior. That is affected by several things, such as:
*) What impact, including visual, would you have on others?
*) What impact would there be if everyone who came here did that?
*) What proportion of the dead wood nature produces in a year would you (or everyone collectively) be burning?
When I was growing up I was taught to use standing dead fuel, and that is what I did. A lot fewer people then, and I was in heavily wooded less traveled areas.
Today, most people are traveling in areas where a lot of others also travel -- and if everyone did that the result would be (at best) ugly. We have all seen campsites where every lower branch within visual range has been stripped from the trees. We have also seen areas where there are no longer any scenic snags.
Furthermore, much of the travel is in areas where people doing that would overwhelm nature's ability to generate more dead wood. (As one example, that is why fire bans above treeline, regardless of how wet/dry it may be.)
Hence LNT, and the "dead and down" rules -- that would have made no sense where/when I grew up, but that make a great deal of sense in the areas many people go today (especially our mountain parks).
The chances are you are not the only person in a huge wilderness, and in an area where nature is producing lots of dead wood every year, so it would be wrong to behave as if you were.