Is that surprising though? There's a strong correlation between pay and intellectual ability/education. There aren't many dull, uneducated engineers, doctors, lawyers, or executives.
If intelligence is at all heritable, you'd expect to see this. If educated parents tend to push their own children to become more educated, you'd expect to see this.
I wonder what the chart looks like broken down by where parents went to school or some non-financial metric. I would bet the children of well-educated college professors or journalists also score well, despite growing up with a more middle class household income.