I agree, Seatle should win this game. There are two things to consider however.
1. Washington had demonstrated the ability to score 40+ points in a game a few times this season, and they are a Joe Gibbs team so today was the exception not the rule.
2. Seatle is Seatle. Meaning they are there own worst enemy when it come to playoff time (or a game to qualify for the playoff). They're expected to win, so all the pressure is on them.
With that said, I'm still picking Seatle to win. If your looking for an upset pick, this is probably as good as any in the NFC. In the AFC, I wouldn't bet against New Engand, those bastards. Probably not even against Indy.