These people have spent what.... a year, almost two in this mess?
Barely a full year, given we know Judith was conceived around the apocalypse (either before with Rick, or after with Shane), and since pregnancy lasts about 10 months, and the baby is maybe a month old at most
, it can't have been more than a year since the beginning.
Otherwise, you're right. Survivors would have to learn quickly - slow learners would perish at the hands of the shambling corpses.