Verlander's in his accustomed spot, but Fister and Scherzer were pushed back a spot because both pitched in Game 5 against the Yankees. This isn't a big problem, but all things being equal you'd probably rather have Scherzer starting twice instead of Porcello. The latter is a ground-ball pitcher, which theoretically will play well in Texas, while Scherzer's Game 4 start will come in spacious Comerica Park.
Also, Scherzer should be available out of the bullpen in Game 6 or 7.
With all four Tigers starters being right-handed, we'll probably see a lot of Rangers outfielder David Murphy and first baseman Mitch Moreland, both of whom struggle against lefty pitchers but fare well enough against righties.
Update: Okay, forget some of that. Leyland's changed his mind, is flip-flopping Porcello and Scherzer. This probably makes sense, overall-talent-wise. But Scherzer might be challenged to keep the ball in the ballpark.