Different people take stress differently. To some there is a great deal of stress in making a major life decision at the age of 18 ... what career they want to follow, without really know what it's all about. There's also stress about final exams, and the major life change of living away from home. Some deal with it better than others.
Not all, but some 18 year olds have a lot of trouble with the responsibility that is suddenly dumped on them at that age, and the future scares them. Suddenly the safety of being a child is pulled out from under their feet. Sometimes too parents don't help, I've seen cases where they will over-protect a child right until they turn 18 and then practically kick them out the day after as they are an 'adult'. If there's any level of this harshness it can really screw up a kid.
I agree that you would be at a different level after a year out, although this depends on what happens in the interim. From what I have seen though, it helps people to learn a little more fiscal responsibility, and if they get what can be termed a 'proper' job (i.e. not a McD's or something like the schoolies get) then it can really boost their social interaction abilites, and general life skills.
As for sitting in the pub .... the place I went for that year was nothing like any student's pub I've ever known!
Not sure how it works over here, but back in the UK when I was at that age, you could arrange your uni course just as if you were going straight in, but make it the following year. That way everything is sorted out, and the chance of postponing/not going is less.
