Well that's very zen of you Gumbafish, I suppose I should contribute just a bit more
It ought to be apparent that I do find these armies very cool, yes indeed. But there are plenty of other armies that I find equally cool, but that don't carry the same sense of *insert term here at conclusion of thread*. So my thought is that those don't have the 'something' that I'm trying to put a name to. The similarity, you see, is ineffable.
Darklighter, that's an interesting word I had not thought to use. Confidence. Specifically a hobbyist who knows their ability and uses it effectively. These armies do have that in common, certainly. I don't know if that's 'it' or not but it's certainly a factor.
GKTerminator, that was as far as I got too. For me, it has a lot to do with posing of models. I find that to be a defining aspect of a great model - a believable and interesting pose. It's not only about dynamic posing though, and I don't mean dynamic in the sense cartwheeling guns akimbo, but 'dynamic' in the sense of at-least-some-thought-given-to-the-posing-of-the-model.
Maybe that's the word I'm after. Believable. As in 'assisting with the suspension of disbelief'.
What I mean is, when I look at those threads I don't see models. I see Space Marines.