The 2005 Sox got outstanding starting pitching and magnificent relief work, in many cases from pitchers who had career years in 2005.
The pitching was helped by excellent fielding.
The 2005 offense generally scored just enough runs to win, because when the homers weren't flying they could still manufacture a run.
After 2005, KW made all the right moves in an effort to repeat. He added a durable quality starter, a LH slugging DH, and a versatile bench bat who had started elsewhere. At mid-season, he added a reliever who pitched great down the stretch. These moves just didn't work out.
The universe is the practical joke of the General at the expense of the Particular, quoth Frater Perdurabo, and laughed. The disciples nearest him wept, seeing the Universal Sorrow. Others laughed, seeing the Universal Joke. Others wept. Others laughed. Others wept because they couldn't see the Joke, and others laughed lest they should be thought not to see the Joke. But though FRATER laughed openly, he wept secretly; and really he neither laughed nor wept. Nor did he mean what he said.