Most runners I know are fully aware of how many miles per week they run. 70 miles per week means you averaged 10 miles per day. 100 miles per week means you are hitting close to 15 miles per day.
I like the idea of a 6 day running week, especially for young runners and those 40 and over that perhaps could perform better with a little added rest. Here is how it works:
Run 60 miles in 6 days with a day off and you've averaged 8.5 miles per day for the week.
Run 60 miles in 6 days and you've averaged 10 miles per day. Sounds a lot better.
In marathon training, most runners probably benefit by taking the day off following the weekly long run. By using a 6 day week, you resist the temptation to run just for the sake of adding to your weekly mileage total.
Just a thought.