This is a common mindset for super-efficient and self-critical people! I very much doubt it is the truth, just Rubinstein (despite his greatness) being a little bit insecure. I really doubt that any harm can come from not a practicing an entire week or a summer vacation lol. Us pianists are so neurotic 
It was not Rubinstein who said it. I don't remember who it was, but it wasn't him at least.
I have often been forced to take breaks in my piano playing, due to my work and other activities, as I am an amateur player. Then I usually need a day or two to get back on track, but I also usually find that many things have matured quite a lot during the absent time. I got a muscle inflammation some years ago, due to over-enthusiastic practicing. (I was a rebounder who just had picked up piano playing again after decades of piano hibernation.) I tried every trick under the sun, including "one week of resting". Nothing helped, the pain just increased. I was really desperate for a while.
Then summer came. It was a hot summer. For over a month I did not practice at all, because it was too hot to do so. Well, it was nearly two months. When I picked up piano playing again in late August, I feared that I had to start all over again. Oh no. I was fiddling a bit for some days, then I found that I played better than before, and the pain was gone.
Conclusion: even a piano player needs a vacation sometimes. There are many romantic myths around pianists, and the "you need to practice for 10 hours every day from the age of 3" is certainly one of the worst. No, you are a normal human being and you need to live a normal life. Even God rested on the 7th day, right?