Surprised by the recent (better) play of the Red Sox?
You shouldn't be. I find it interesting that baseball fans often talk about three "phases" of the game: pitching, hitting (or offense), and defense.
I don't look at it that way - there are only two, and I will tell you why - you can't intelligently separate pitching and defense; they are the left and right hand of the segment of the game in which you try to prevent your opponent from scoring runs. You prevent them from scoring runs by making it as difficult as possible for them to hit the ball, and by effectively catching it as often as possible when they inevitably do hit it.
The infield defense is much better with Mientkiewicz at first (the play stabbing last night in Chicago, for example) and a healthy Cabrera at short - compared to Millar/Ortiz and a hurt Nomar.
Why does this team look so good right now? For the same reason they looked so bad 5 or 6 weeks ago - for most teams, everything starts with stopping the other team. Players spend less time on the field. Players get less frustrated, they feel more confident. The pitching becomes more aggressive in going after hitters. You are playing the game of baseball as a whole - not just participating in a glorified batting practice by slugging doubles off the wall.
Manny has been hitting, yes, but how much of his resurgence came from the great fan reception he got at home last week after some spectacular catches he made in left? I think Manny is much more proud and satisfied (and motivated) with a great catch than by slamming another 450 ft. HR.
And so is the team, overall.
It is a better Team.