I completely agree that assistant jobs are stepping stones. They were always considered educational opportunities back in the day when I had those positions. An assistant made more money than a working student, so it was a good gig to get more experience and be able to pay some bills–but not many. And, no, you didn’t have to be independently wealthy, just super frugal and never have your own horse. There was no real insurance, but they had to have Worker’s Comp and there was an assumption out there that since you were living and working at the barn (mine always included housing) you were most likely to get injured on the job and would thus be covered. It was cheaper than college and looked 100x better on your resume to note who you had worked with/for rather than saying you’d sat in a class about horses and were riding college donated horses. Top horses at a top barn were the things that allowed you to charge higher training fees. The kids out of college were usually laughed at and paid even less, since most had no real world experience.
For those talking about jobs that pay so little and don’t have housing…you’re looking in all the wrong places, or you don’t have the correct qualifications–nor do you have the right connections. It’s 80% networking (who you know) when looking for jobs in the horse world, and 20% being in the right place at the right time. Along with that, it’s having paid your dues. No one thinks they need to pay their dues anymore. Yes, I went to college, but that is not real world experience and it seems only the horse world recognizes that. In corporations people get a four year degree and get offered jobs they have no practical experience in (most of the time) and are paid better than in the horse world. Go that path if you don’t want to have to pay your dues and make next to nothing. It is easier, and you’ll be just about as broke until you’ve paid off your college debt. 
The thing everyone takes advantage of in the horse world is the love of horses. And I don’t see anything wrong with that. It’s hard, dirty, and dangerous work. But we do it because we have a passion for it first, not because we think we’ll make a fortune out of it and put in a 40 hour work week. Horses are 24x7, not 40 hours. You choose the life of working with horses, or you don’t. And sometimes you have to try it on for size to decide if it’s worth it to you or not. (And sometimes it’s worth it until you decide you want other things in your life…family, kids, a house, your own horse, etc.) Every once in a while someone has enough skill (or is crooked enough) that they make a fortune in the horse world, but those are few and far between, and they still put in a TON more than 40 hours a week.
It’s a unique industry and I like it that way. It helps separate the wheat from the chaff. 