Interesting question Injury Advice.
I think you are proposing that runners might be more likely to drink excessivley compared to the average population due to a natural predisposition towards chemical dependency.
Whether its the endorphins from running, or alcohol, to the brain its just another fix.
I vaguely recall one anonymous forumite admitting having swopped one addiction for the other (the later one being running).
There must have been some studies on this?