If anything, the fact that writers pace about proves that their minds are functioning, either contemplating all of the words to be written down or to be avoided. While progress is not made on the paper, it does not mean that progress is not made in the mind.
If a writer is not day-dreaming, he is dreaming the inspiration for his novel the same way Robert Louis Stevenson came up with nothing to write about until he dreamt of Dr. Jekyll and Mr. Hyde. As such, if the process of formulating what words to write involves an unconscious part of the mind, then this process is beyond the control of the writer. Creativity is not a phenomena to be forced, rather it is processed through repetitive thought and the distractions could become inspirations. It can only require spontaneous moments of epiphany in order to conceptualize new, original topics to write about.
Procrastination can be an ordinary part of a writer's life, especially if it is used in a way of managing anxiety and fear of failure when it is hard to materialize a story out of nothingness. So it is unlike what King Lear would said, "Nothing can come from nothing." The process of writing is just too complicated to pinpoint and procrastination seems to be a major component. It is not one that would be readily accepted nor is it desirable but it does help facilitate the thinking process.
However, the production of idea invention can only be stimulated by the increased activity in the frontal lobe. Originally, the brain activity was thought to have been divided between the left and right sides, but when it involves creativity it mainly has to do with the connection between the temporal and frontal lobe. This is how exercise, phototherapy, and a functioning dorsolateral prefrontal cortex (responsible for working memory and flexible problem solving) can help with depressive and non-depressive frontal lobes that have lesions that can result in a decrease in writing ideas.
Since it is hard to expect any productivity from an unproductive circumstances such as the delay of idea invention, I would expect there to be more research into this issue. However, the issue remains that writer's block is a completely normal part of the writing process and is to be expected. When it is expected, then a cure for it would also be already planned.