Not continuing production after 13 episodes isn't necessarily a death-knell, although it depends on the announcement itself.
A to Z and Bad Judge were both shut down after their 13 episode order. So, it'll be more like A to...M. They were announced as canceled, basically, and are unlikely to see new seasons. Constantine, though, has seen its ratings improve. NBC might be willing to give this one a shot. Grimm started somewhat slow, but picked up steam, and to be honest, there's nothing wrong with a solid 13-episode season. 22-episode runs are "full" seasons, but several shows (e.g. Hannibal and a TON of cable programming) are 10-13 episodes now. If the writers could plan for a 13-episode season, then the seasons themselves could be quite good.
Anyway, guess we'll see.
Personally, especially when you look at Constantine's DVR numbers (which are almost as good as its broadcast numbers), I think it just kinda highlights how traditional ratings systems are ill-equipped to gauge popularity anymore. Very few people that I know sit down and live watch TV as "appointment" TV anymore.
