I've done a few 100-milers, but never more than 130 miles in a single week. Personally, I'd prefer the 100 in one day option.
Doing 100 in one run feels like an actual accomplishment. It is psychologically appealing based on our love of round numbers. And while it may seem like a long time on your feet, at least you get to finish it all in one fell swoop.
The 140-mile week is just such a drag, with no clear reward at the end. For a small percentage of runners, it would probably be good solid training, but most of us would just get worn out, achy, and sick of it.
Another advantage to the 100 miles in one day is you can take a day or two off work, or even do it on a weekend without missing any work. With the 140-mile week, it's not really enough to justify taking the week off work, but at the same time, it would get to be really tedious trying to fit in 2 10-milers a day around work, family, etc.