Because I am Joe Girardi. You've never seen him in the dugout with his blackberry out?
Anyway, they never have in the past. Every single time they've been in this position, they've done exactly what I just said. Granted, Girardi wasn't the manager, but he's been part of this team in the past. I see no reason why things would change.
Also, I believe it's common, at least with teams that have high expectations, not to celebrate in that scenario. When the Mets clinched the wild card in 2000, they didn't celebrate because they were still contending for the division. Once Atlanta clinched, they celebrated their successes.
What'd the Red Sox do in 2007?