Moderate drinking has a lot proven health benefits, I wouldn't be surprised if the positive affect on blood vessels can lead to an increased blood flow to the brain that could help concentration.
The problem with alcohol though is that it's too socially acceptable. Other drugs get people on your back quickly, telling you that you have a problem and the stigma makes you conceal it, feel guilty about it earlier. With booze it's easier to go from moderation to too much without people noticing, no one will get on your back until you have a proper problem.
Many people have no problem with alcohol, enjoy it moderately but there is always that danger and the people around you won't help you until it's too late.