I have ADHD, and let me tell you, from a 2nd person point of view, it may seem nicer when we're not medicated, but I myself prefer being medicated and controlling myself... I'll give you a couple of examples as to how this affects our attention span:
1) In a math exam I had last semester, I was using my calculator to find the answer for a couple of trigonometry problems. First problem, done SO FAST without the calc... 2nd, same as first... By when I was halfway done, I stumbled upon a problem that gave me a weird answer. I thought to myself "This problem seems kinda weird... I'd better try with the calculator". I started hammering commands into it, trying to find ways of how I can answer the problem AND write down the process. While I was doing different ecuations, I started trying to find answers to previous problems, trying to remember problems on my notebook, trying to find the answer to imaginary problems... I even learned how the other buttons on my calculator worked from playing around with it! I noticed I wasn't doing my exam when I had to give it in, and I got a pretty bad grade because of that. Had I been medicated by that time, I wouldnt've lost my concentration so easily.
2) When I'm talking to people about something they don't understand fully, i try my best to explain it to them the simplest of ways so they don't miss a detail. Sometimes I try to explain it so well I completely forget what it is that I was talking about in the first place. Imagine this during oral presentations, or while explaining physics to friends, or helping them with school problems, or anything else that might require extensive thought... It might seem like a funny situation, but there's nothing funny about getting a bad grade or bad job interview due to getting derailed from the topic while talking.
3) My mind is ALWAYS running. It takes me like 3 hours of rolling around my bed before I'm finally tired enough to sleep, because I'm so jittery and full of energy and thoughts that I can't keep myself relaxed. I always find myself thinking about current problems, my future, what to buy with the money I'll be getting, how my life would be with a family, even SCIENCE is something that whirls around my mind every night! I bite my nails more often than a normal person would when stressed, and find myself biting my lips and ripping off skin without noticing I'm doing so at times. Thinking about sexual relations and anything else an adult thinks about, while trying to fall asleep will most likely keep YOU awake at night, too. Unlucky for me, I don't have that 'switch' which should make it easier for me to catch a Z or two.
I forget I have homework, forget I have appointments, forget I have (had, now) medication, and forget I promised people stuff, because I don't give my promises the attention they should receive for me to remember them when I need to. I don't remember what I did a week ago, only the major details. I can't even remember what I wore the day before yesterday, that's how amazingly annoying this is! I've even started writing text messages to send people, only to start thinking of what I want to eat midway then closing my cellphone and deleting the whole message. And this is just my short attention span, imagine my overflowing energy!
I seriously believe it needs medication in order for the person to really have a chance at a normal life, which is something I wish to have access to. Sure, medication is not a MUST, as it is not a life-threatening disorder... But in a social viewpoint, it is. I used to get medication, but got off of it because my parents started yelling at me and stating that I would become an addict, and they'd NEVER leave me alone about it. Once I turn 21, I'm going to see a psychiatrist by myself and keep the pills a secret.
ADHD in people can also be the catalyst to several psychiatric conditions, most common being depression and anxiety disorders. I never got to clarify with my doctor, but we discussed that I may be also suffering from a form of depression (either I'm hypomanic, or it's silent migraines that make me change the way I act at times, since I get those officially).
tl;dr: I believe it needs medication. It's not a MUST, though, you can live without it, but you won't have the highest life quality you can achieve.
EDIT: GOD!, science has come to understand how the brain works pretty well, just not as much as they understand every other organ in the body. The brain is much more complex than today's computers, but we have an idea of what it does, how it controls things, what areas of the brain have to do with our actions, and other such basic info... We also have an idea of what causes ADHD, which is practically an increase in the production of some of the brain's chemicals: it's a biological defect... Medication should be given not when the case is too extreme, but before the case REACHES said extreme, since it's made to prevent, treat, control and/or cure physical/mental problems... And yes, we ADHD sufferers need more outside time. But in the end, it's not the answer to our dilemma. When I was a kid, I was in baseball, basketball, volleyball, swimming, tae kwon-do, and track-and-field. Didn't do much in the long run...
I guess some people just grow out of ADHD, and others don't. I'm one of those that still hasn't grown out of it.