From ESPN:

Saunders didn’t get to pitch in the ALDS series against the Red Sox, because it was a sweep. The Angels want Saunders to pitch in Game 2 both because he can help neutralize the short right field porch better, and because Jered Weaver, who will pitch in Game 3, fares much better at home.

The worst thing you can do is make judgments about players based on small sample sizes.

Jered Weaver has a better ERA at home compared to on the road this year (2.90 home vs. 4.78 away) and last year (3.71 home, 4.91 away). Yet in 2007, his road ERA was lower than at home, and in 2006 it was 2.91.

Here are his career splits:
At Home: 7.3 K/9 2.1 BB/9 1.0 HR/9 1.17 WHIP
Away: 7.3 K/9 3.1 BB/9 1.1 HR/9 1.33 WHIP

In other words, Jered Weaver is a pretty good pitcher, regardless of where he’s pitching. The differences in ERA could be attributed to many things, but his peripheral stats are pretty much the same in both places.

Joe Saunders, on the other hand, is a soft-tosser who depends on hitters making contact. Against a lineup that potentially does not include a single below-average hitter, this could be an absolute disaster. Furthermore, thanks to having four switch hitters in the lineup, Saunders would only face three lefties, so neutralizing the porch isn’t so much of an issue.

Even worse for the Angels, starting Saunders in Game 2 likely takes a start away from Scott Kazmir, who, despite having some issues, is clearly a better pitcher.