Those figures won't be that far apart. It will somewhat, because higher incomes will have a bigger house and more luxurious car. However, they're putting more of their money into investments, not cost of living.
And I'll reiterate, that's the average for one person, not a family.
Why I change my own oil. Not because I save money--generally don't even before your time is factored in--but because I know how to put on an oil pan bolt without cross threading it.