If you were going to compare a neglected indoor rabbit with a neglected outdoor rabbit, the outdoor rabbit would be slighly better off because of the outdoor smells and they would have a better chance of being rescued because they might be in view of others.
I have heard of no non-bias studies on the life span of rabbits, so I don't think anyone really knows which rabbits live longer.
When it comes to keeping rabbits, most people model what they see, so if keeping one rabbit alone in a hutch is what people grew up with, a person might think that is the way rabbits should be kept. If you keep your rabbit inside, you teach your family how to take care of rabbits, but if you keep your rabbits outside, you teach the whole neighborhood, good or bad practices.
There are pros and cons in keeping rabbits outdoors and indoors. In my situation, keeping my rabbits outside is better because my dogs wouldn't leave them alone. I keep their hutch inside a pen where they can't be harrassed by dogs and have a quiet life with plenty of room to run. We live in a small house where there would be no room to run inside, unlike outside where they have a large pen to play in.
I think there is really no good answer to what rabbits live longer, those who live outside or house rabbits? It is one of those case by case things. I rescued my rabbits from an abusive house (inside), and I love keeping my rabbits outside because I love being outside. Most rabbit people I have talked to tell me that I will forget about my rabbits outside and neglect them, but that is not my experence.
Let's face it. We don't all have the same kinds of homes, families, environments etc., so outdoors or indoors, I think the rabbits that live the longest are the ones with the best care, and that would take a case by case study. We would have to compare well cared for house rabbits with well cared for outdoor rabbits to get the answer. Many times people have compared outdoor shelter rabbits with well cared for house rabbits, and that isn't a fair comparison, because it leaves out all the abused and neglected house rabbits that are not brought in by animal control because they remain undiscoverd in homes.