Offer your thoughts or opinion on the input financial query or topic using your financial background.

Why is the highest quintile the only quintile whose wealth exceeds its income? 
There are a lot of forces at play here, one of which is addressed in your second bullet point. Housing, transportation, food, and healthcare are pretty much the staple expenses of a modern day human.  While these expenses all have a range from minimum required to function and luxurious all humans incur these costs.  The lower rung wage earners earn an amount closer to their actual costs than higher earners.  As income scales up these expenses typically also scale up with different lifestyle choices.   There reaches a breaking point though where is so much excess to your income that you begin meaningfully spending on investments; you may also begin to take a meaningful portion of your compensation in securities rather than currency.  In times where the economy is booming, folks who hold assets in securities rather than currency really win.  In 2008 people in that highest rung really took a wealth hit (and probably an income hit).