The Steelers reached the decision to start Roethlisberger before the Ravens' 34-14 loss to the Chargers that allows the Steelers to win the division title and get a first-round bye if they win their remaining three games.
Roehtlisberger has a Grade 1 ankle sprain and didn't practice all week until Saturday, and even then on a limited basis.
Steelers fans have been on pins and needles about Roethlisberger's status for the past week, but honestly, it comes as no shock that he's playing. Even if the Ravens hadn't won, the Steelers would have had a lot to play for at this point, and Roethlisberger seems to be willing to play through all sorts of pain when there's anything at all on the line. It remains to be seen how effective he'll be, or how his status will affect the Steelers' play-calling.
With the Ravens' loss against the Chargers, the Steelers currently have a half-game lead in the AFC North, and they can take control with a victory over San Francisco, which would also give them a decent shot at the No. 1 playoff seed in the AFC.
For more on the Steelers, check out Behind The Steel Curtain.