Nelson, while I appreciate you having your opinion on caliber over shot placement, and being able to articulate why, I respectfully disagree. For me personally, shot placement trumps caliber. I can see terminal ballistics being more forgiving for a lack of shot placement, but not so much so that it would warrant me buying another rifle. I find the 5.56 plenty capable in my hands.
And with respect to the "all of the conditions hunters experience," again I respectfully disagree. As a hunter we have the ability to create our own conditions. If the weather is freezing and I am shaking....I don't go out or I don't take the shot. If I can only see my game from off-hand and my sights are moving....I don't take the shot, find a more stable shooting position. I pass on a lot of shots some would take because I am working within the confines of my equipment and skill.
You also went on to mention that this thread is really about finding the right equipment for the job. To which I find this thread to be somewhat misleading.
The original topic questions that you posted are, "I've known a few that use calibers like the .223 and .22-250 Remington for deer, but why is it so rare compared to the masses using larger calibers? Is this a regional thing and I am just unaware?"
The short answer to the above question is probably something to the effect of, the person behind the counter hands them a 30-06 or 308, or their buddy recommends one.
I am just adding my experiences to the forum, since I do use 5.56/.223, and I find it works perfectly well. It seems like you have a bone to pick with lighter calibers. Seeing as how you feel the direction of this thread is finding the right caliber for the job, implying that lesser calibers are wrong for the job.
If you only have one rifle, you make it work for the task at hand.