The Nats management made the decision to limit Strasburg's innings well before the season started and well before they locked up a playoff spot. There's no way they could foresee the team would do as well as they did. Many preseason predictions had the Nats doing better, but playoffs were iffy at best.
Given the decision to limit his innings - which was made before the season ever started - where I really fault the Nats management is that they didn't attempt to ration or manage those innings at all. They basically pitched him until he used them all up - and then sat him down. Had they planned ahead, perhaps he could have had some of those innings left for September and the playoffs.
Looking at his game log from last year - http://www.baseball-reference....mp;t=p&year=2012 - you can see he started opening day and went 7 innings. Then he pitched nearly every 5th game until they sat him down. Start with the easiest solution - don't have him start the season until the 10th game - that gets him two more starts in September. Don't have him go 7 on a regular basis - make his normal start early in the year 5 innings. Use the all star game break as a means to skip another.
Perhaps by doing this they drive him crazy - or aren't in contention in September - but he has innings left to spend at the end of they year.