We all know that the Nationals' pitching has been good, but maybe we don't realize how good it has been.
Baseball Prospectus (http://www.baseballprospectus.com) ranks pitchers by various measures, one of which is VORP--Value Over Replacement Player. VORP calculates a player's contribution over that of a replacement-level player at the same position. Roger Clemens, not suprisingly, is first in the National League, but 3 of the Nationals' 5 starters rank in the top 11--Livan Hernandez (#7), John Patterson (#9), and Esteban Loiaza (#11)--and Chad Cordero is #25.
No other team has 3 pitchers in the top 11--the Houston Astros have 2.
Cordero also is #1 in BP's ranking of Relievers Expected Wins Added, which measures the expected wins a relief pitcher adds over a replacement level pitcher.
These four pitchers are a very big reason--maybe the biggest reason--why the Nationals have done so well in the first half of the season. And whether the Nationals continue to perform so well depends in large part on these pitchers continuing to pitch at a high level.