Occupation, education, income, and wealth aren't purely based on choices though. However, if you do think about each in a vacuum, what's interesting is class used to be based/weighted quite a bit more on wealth, specifically inherited wealth. Not so much anymore, and one argument to explain this is increased education.
I have little wealth (inherited or otherwise), and even though I'm upper middle or higher in occupation, education, and income, I still only hit around 70/75 in class overall.
It is really interesting.