First things first : Rick Short!
A week or so ago I brought up you that I felt Elijah Dukes was the key player for the Nats to move forward on offense. There was supposed to be a follow-up with a "pitching key" but the more I looked at it the more it became apparent there wasn't a single player who would be the pitching key for this season.
Sure, it's important that Straburg develops into a very good pitcher, but it's not so much important this season. Let's say he starts in the minors (very possible), struggles a bit so he's not brought up until July (sorta possible - he doesn't have to struggle too much for them to justify this), and for the second half of the season he pitches with a 3.80 ERA mostly showing off a world-class arm, but also having a couple of crash and burn starts in there. To me that seems to be an acceptable scenario even though that's not helping the 2010 Nats too much. The Nats shouldn't be depending on Strasburg to drastically improve their rotation this season. It could happen, it probably will happen, but they shouldn't be relying on it. Strasburg is a key for the Nationals franchise, but he isn't a key for the 2010 major league pitching staff.
I guess Lannan and Marquis may be keys, but I don't think there's a big question mark hanging over them considering what the Nats want. Can they each give the Nats around 200 innings of around average pitching? It's like asking Dunn if he can give the Nats a 140 games with good power, like saying for the Cards to be good Pujols must be great. It should happen. If your key is player X doesn't drastically underperform then every starter is a key (which I guess is true but that's not what we're looking for here)
What is a key for this season is having someone to pitch well enough beyond Lannan and Marquis to hold down a spot in the rotation all year. They need someone to stabalize the middle of the rotation and to help ensure that the bullpen is not overtaxed as it has been in the past. But whether this pitcher is Strasburg, or Livan, or JD Martin, or Matt Chico or etc. etc. etc. doesn't really matter. There isn't a key player as much as a key result.
Another key is finding three decent arms for the pen from Day 1. That shouldn't be too hard, but the Nats failed on that front horribly last year, so Nats fans shouldn't take it for granted. With three reliable arms off the bat, Riggleman can hopefully find other decent arms for the pen during low pressure situations over the first month or so without jeapordizing what wins the Nats have lined up by the 7th inning. It'll matter that who the Nats name closer is one of the three that do well, but who exactly the closer is doesn't matter. If Capps stinks but Burnett, Clippard, and Bruney are fine, the Nats should be ok. If Storen struggles, but Walker, Stammen, and Bergmann pitch well, the Nats should muddle through. Again key results but no key players.
The Nats desperately need better pitching in 2010 and they've lined up the players to make that happen, but there is no individual arm that could make and break the Nats.