"The Office" renewal was the least surprising of the three, as it's the only one of NBC's comedies (including "30 Rock," which was already renewed earlier this season as a salve for being moved to 10 p.m.) to actually be successful on its own. So it was almost certainly going to come back. But nobody knows what the show will be like once Steve Carell is gone. (Of late, I've been of the opinion that things might actually get better, as the show has mostly been in a rut the last couple of seasons.)
"Parks and Rec" (which, as I noted this morning, has a fantastic episode on tonight) was a decent bet to come back, but not a lock, as its retention of its lead-in audience from "The Office" has been acceptable but usually not much more. But it's been great all season (and last season), and should get a bump from the overall interest in Carell's farewell episodes of "The Office." A new audience is coming slower to it than I would've liked, but I still think it's NBC's best long-term bet to succeed "The Office" if the post-Carell era is bumpy.
"Community," meanwhile, has been getting clobbered on the left by "The Big Bang Theory" and now on the right by "American Idol," but its own audience hasn't fallen off as much as we might have feared going into this season. Its audience is its audience, and as Bob Greenblatt looks to rebuild NBC, it makes sense that he'd bet on a quality show with a steady (if small) audience rather than bank on lots and lots of unknowns for next year.
Excuse me while I go do a dance of joy. "The Office" is a rerun tonight, but all the other NBC Thursday comedies (including the unrenewed "Perfect Couples" and "Outsourced") are new tonight.