What do all these living rooms have in common? Aside from a vibe and palette that I love, they all feature area rugs on wood floors. The rugs are all just large enough to define the sitting area while leaving the floor largely exposed. We have been talking about a larger scale rug that almost mimics wall-to-wall carpet. I think a smaller rug has the effect of focusing the room and creating a cozy area for hanging out, while making the rest of the room feel expansive.
Also -- and I think this is not a small consideration -- sweeping or swiffing is so much easier than vacuuming, and therefore could be done every day rather than once a week, so I think ultimately the living room would be much cleaner. I must add that I am speaking as the person who will be doing most of the cleaning.
I know most of these living rooms are not brownstones and have very different dimensions and layouts from our house, but I think you can get the idea of grand space vs. cozy delineated seating area. Imagine the bottom photo if they had a huge rug over everything instead of that small one that creates a special space. I think it would lose something.
Also, this way we could go with a more exciting rug if we knew it was possible to keep that area off-limits to dog and messy stuff. If we cover the whole floor, we just have to pray never to spill, but if we differentiate this one area, I am more confident that we could keep the dog out of the danger zone, and then we can pick something lighter or plusher or fancier or whatever. Then the problematic big box of a parlor floor becomes two nice areas: living room and dining area.