Simple as that. The Nats are at home for the next 6 games. A good team facing these fair opponents, would expect to go 4-2 during this time, and preferably not 3-0 vs the D-backs and 1-2 vs the Phillies (though I'd still take that, if I were a Nats fan).
Offensively, the Diamondbacks are a team that can score some runs, and currently they could put together a whole lineup of guys hitting well. The only guys struggling are Ryan Roberts and the guy you heard about maybe in all those Tyler Moore notes, Paul Goldschmidt. However a strangely hot Lyle Overbay and a Cody Ransom swinging from the heels can take those spots. The Nats pitchers haven't faced many decent lineups. In fact they've only faced one team with a R/G significantly above the league average. However, that was Houston, and they held them to 5 runs over 3 games. The Astros averaged 4.6 R/G before the Nats and 5.3 R/G since so the Nats pitching staff passed that first test with flying colors. I'd bet on them again this time.
At the same time the D-Backs pitching staff hasn't been great, but unfortunately the Nats probably won't get to take advantage of that. They miss the D-Backs back of the rotation and the worst of the pen, Joe Paterson, was sent down a week ago. They'll face decent pitching, but in my mind a decent team should be able to manage to score some runs against these guys. If the Nats get shut down again you'd have to be disappointed. I'd want at least one 5+ run game here.
The Phillies, if you don't know, have crashed and burned offensively. Ruiz and Wigginton are carrying them right now, with Polanco finally getting hot. But you can't feel good about an offense where the big names are Polanco, Ruiz, and Wigginton. Pence, Victorino, and Rollins, might bounce back, but those first three won't stay hot. They need Utley and Howard and they won't have them for this series. The Nats, led by Strasburg and Gio, should definitely shut them down.
Pitching wise the Nats catch a break here. They miss both Hallady and Lee. Hamels and Worley are no slouches, but if you had your choice in a 3 game series vs the Phillies you'd go with those two over Halladay and Lee. Outside of a couple arms, the Phillies pen has been pretty weak, so if the Nats can stay close (and really why couldn't they) you'd have to like them to score more than the Phillies in the late innings.
So what do I see? I do see 4 and 2. Problem is I don't see any blowouts here so every game will be close and close games are hard to pin down. A couple hits/outs go the wrong way and 4-2 is 2-4. If you ask me, though, the most likely way they'll get to 4-2 I'll go with this scenario - Nats lose 2 games to the D-Backs, but sweep the Phillies. I think Nats fans would take that.