This is a good question.
I would say that, for certain, 100% productivity is impossible. In college, they actually taught us that as Graphic Designers, our productive time is only about 60%.
If you provide an invaluable creative, or technical service, does it make sense to work under the same terms as someone who bags groceries? If you think so, please come work for me, and I will pay you very little money to pour out amazing technology and design at an unfair rate, so that I can profit readily.
Often, my productivity time (which I count as actually being in the zone, totally focused, working on a product) is no more than 15%.
There are two kinds of workers, I've found, shotgun workers and sniper workers.
Shotgun workers are productivity people. They get a problem to solve, and immediately they whip out their trusty shotgun and start blasting away at it. They blast and blast and blast away at it, until it's gone. It's of little consequence how much energy it took to actually do. Such workers are usually very good at looking busy and even better at wasting their own time.
Sniper workers prefer to take as few shots as possible. Given the same problem, a sniper worker would probably go to a nice, quiet knoll, overlooking the whole scenario. Then he (or she) will simply lay there, waiting, and considering. They will determine their targets weak point, and then swiftly and cleanly solve the problem. Often, it looks like these guys aren't working at all. But they are!
The big difference is that the shotgun approach doesn't tend to scale well! Once projects get to a certain degree of complexity, the shotgun approach stops working, as it takes a huge amounts of shots to make it work. Sniper workers, however, scale all the way up, and are ideal for solving complex problems.
In conclusion, having lower productive time is good because it scales much better than high productive time. The less of your time you spend actually "doing", while still getting comparable results, makes you more of a sniper-style worker.