That sounds like a highly unusual situation. Most public schools pay jack squat.
That being said, there are a couple of things to consider:
First off, you may live in an area with a high consumer price index. I'm sure people can get by just fine on $80k, but it may not be as much as it sounds like to someone from, say, the midwest (my understanding is that most of California is this way, but feel free to link your actual county if you want to prove me wrong about your specific situation). Most likely the teachers at your charter school are underpaid and not living particularly comfortably.
With respect to your charter schools getting slightly better results, it's important to consider the fact that it's generally more affluent families that can afford to pay extra to send their children to a non-public school. Affluent parents tend to have more free time to spend with their children, and can afford to be more involved in their kids' lives, which means they can push them to study, do their homework, etc. On average, kids at public schools have parents who make less money, and are more likely to be raised by single parents. Blaming the difference in performance between public and private schools on public school teachers is problematic unless you're also correcting for socioeconomic factors.