Yes, except Riggleman is one of the all-time worst managers relative to his team's Pythag. You can book it that his team will finish 3 or so games worse than his pythag every year. That he's piled up his 3 games this fast is the only surprise.
You are right, the Nats finished 3 games worse than their Pythagorean w/l last season.
This is kind of shocking, but the Nats finished 7 wins behind their Pythagorean prediction in 2009.
This is a small sample size, but it is still interesting to note:
In 2005 under Frank Robinson, the team finished 4 wins ahead of their prediction
In 2006 still under Frank Robinson, the team finished 1 win behind
In 2007 under Manny Acta, the team finished 3 wins ahead
In 2008 under Manny Acta, the team finished 3 wins behind