Yes, there's a reason for "won't work."
This is the original wording, from Frank Lewis Dyear and Thomas Commerford Martin's "Edison: His Life and Inventions," 1910:
"I said: `Isn't it a shame that with the tremendous amount of work you have done you haven't been able to get any results?' Edison turned on me like a flash, and with a smile replied: `Results! Why, man, I have gotten a lot of results! I know several thousand things that won't work."
Suppose I am trying to start a gasoline engine in cold weather. Perhaps I am trying to start my snowblower by pulling the cord. I pull it once. It coughs and splutters and doesn't start. At this point, I would say "It didn't start." But my work is not done. The result might not be final. Maybe if I just pull it a few more times, it will start. But if I pull the cord ten times and it doesn't start, I decide that the situation is final. I say "It won't start."
Now think of Edison. He wants to make the point that his negative results are still results, and represent progress. In order to make this point, the negative results need to be firm, final.
Imagine him crossing off items on a list. He tries material X. It doesn't work. He wonders if maybe a small change might make it work, if he stretched it tighter, or used a thinner piece. It doesn't. Finally, after several tries, he concludes that it is now final and definite. He has a negative result. Material X "won't work." Now he crosses it off the list.
The number of items that "won't work" and therefore can be crossed off the list represent results. They are not failures, they are measures of successful progress toward a goal.
In order to cross the item off the list, the work on that item needs to be finished. You don't move on to the next until you can say, not just that it "didn't work," but that you are sure it "won't work."