Drunk monks and the 5th precept

I have heard that the 5th precept was not a core of Buddhism, it was created later by the Buddha after some monks returned drunk from alms because they had something with alcohol (accidently I believe) My first question is: Is this story true? Many Buddhist school claim that the problem with alcohol is that it can cloud the mind and make it easier for breaking the other (more important) precepts. Based on that some schools are ok with lay people drinking in moderation, with the commitment of not getting to a point of losing control of their acts or doing something they will regret. So, is drinking with moderation (socially) breaking the 5th precept?