There are plenty of middle class folks in the "biz". These are the makeup artists, sound designers, animators, model makers and so on. They all make a good living pursuing their dream.
The point he's making is that not that many actors make their living through acting. Also, not many people go to Hollywood with a dream of being a gaffer. When you get a union job, you usually live month-to-month since living in Cali can be expensive.
Like with many other "scalable jobs", you have few winners and many, many losers. Acting, singing, startups, CEOs, traders... they all fall into this category.
