I refuse to believe that its that huge of a difference. Maybe if he threw 250 IP, but not 20 extra IP
20 extra IP as opposed to what? There's so much strawman and mindfact in your argument here that it's kind of hard to separate it out. First, let's take a realistic expectation of what he's likely to throw if he gets shut down at various points. He's thrown 140 (actually 139.1) innings in 24 starts. That's just under 6 per start. Let's take an average of 5.83 ip/start, recognizing that noone can actually throw precisely .83 of an inning. From now until the end of the year there are 42 games left. A regular rotation means Strasburg will start 8-9 of them, depending on how the rotation falls. Let's say 8*. So, that means he's got 46.66 IP left in the regular season. That puts him at 186 or thereabouts at the start of the playoffs. So if you argue a threshold of 180, you're shutting him down literally one start short of the playoffs.
If you're saving him for the playoffs, you're doing so because you want to use him. He's definitely a Game 1 starter, right, else why push him? Let's say for argument's sake that the Nats go all the way to the world series. Depending on how many games each series is and what game you choose to start him, he's starting probably 6-7 games. As few as 3-4, as many as 8-9, but let's say 6 as a point for argument. So, more or less two starts per series. Let's assume his IP/start remains unchanged. So that's another 35 innings on top of the 186, or 221. If the Nats get eliminated, it ends up being less than that, naturally. If he goes deeper in playoff games, maybe it's more. But it's not a matter of "20 extra IP." A full playoff season on top of a full regular season would put him at 220 or so, on a young arm that has never gone more than 123 in a season.
Bottom line: If you don't shut him down, his total IP is closer to 250 than it is 180.
*- folks who have argued a six-man rotation - a six man rotation at this point saves Stras 1 start, or 6 innings, at the cost of having John Lannan throw 40-ish innings in place of ZNN, Gio, EJ and Detwiler.
Nobody's saying that his arm falls off at 180 instead of 160. Nobody's saying that he might not be able to go 220 IP. But every inning is a risk. Every inning on a tired arm is a higher risk. Every high stress inning on a tired arm is an even higher risk. Playoff-level stress on an arm that's tired and 80-100 IP higher than it's ever thrown before is an even higher risk. But here's the problem: There is no way to calculate that risk. It could be fine. He might win us the world series this year and do long-term damage such that he's not quite the same pitcher afterwards.
I think too many folks think that this is a calculable risk, when it's not. There is some greater-than-zero chance that he could get re-injured or do chronic damage such that he's a less effective pitcher going forward. Balance that against some greater-than-zero chance that we are more likely to win the World Series with him. Toss a coin, roll some bones and takes your chances and hope you make the right choice, because you'll never really know for sure.
For me, I shut him down at about 165-175. Towards the sooner end if we are maintaining our lead, towards the higher end if the race gets tight. But I get that you might be throwing away your best chance at a WS. On balance, I think I'd rather make sure he's the same pitcher in 2013-15 even if that means next season is a tougher uphill climb. And I get why others might think that's nuts - that you roll the dice the other way, hope he doesn't get hurt and reach for the chance when it's right in front of you.