As I'm sure Cofty, JWFacts and others have pointed out in detail, the JWs have taken the 'abstain from blood' scripture out of context. I think it's to do with God forbidding the eating of blood. The Apostle Paul (who wrote the scripture) had no idea about blood transfusions and so couldn't possibly have had them in mind when he wrote the scripture.
Also, I'm not sure the alcohol-blood analogy is a sound one. Medics used to disinfect wounds by using rubbing alcohol. I'm sure that was still the case when treating an alcoholic's (i.e. someone who must 'abstain from alcohol') wounds. An alcoholic in the past could well have been advised to abstain from ingesting alcohol, yet his wound might have been treated with rubbing alcohol.