Wait what?
I took the chart to mean that if your parents make tons of money, your SAT score is going to be better, not that if your SAT score was good, you will make tons of money. Not sure where exactly that chart is coming from so I dunno what context the axes are in.
I interpreted it that way too, x axis is normally the independent variable
I think you've got it right. Mostly because the writing section was added in 2005. So that would mean that anyone who did better than 560 on the writing is making $200,000 a year at the age of 21. And as a 21 year old who did do much better than 560 on the writing section (as well as the other two sections) I for one am not making $200k+...
Higher SAT scores generally mean better college education (on average) with more scholarships (enabling less student-loan slavery post-graduation), more grad school, better jobs, etc.
People that got an 800 on their SAT (out of 1600 in my day) weren't really on the fast-track anywhere except mowing lawns. The kids pushing closer to 1400-1600 were generally headed to decent schools.