I could make a similar point. I saw very little decline in performance when dropping from 100-120 miles per week back to 60-80 miles per week. As a point of reference, over the past 3 years, at these lower levels, my fastest 5K times have only been 10-20 seconds off my best road times, run at the higher levels of training. Of course, that ignores the fact that I'm still running a minute or more faster than I was (on the roads) when I was training at 60-80 miles per week before bumping the volume up in the first place.
As several people have pointed out to me over the years and I have pointed out to even more people, it's easier to maintain the fitness than it is to get it in the first place.