It works on multiple levels.

http://www.physorg.com/news95074548.html - World's economies show similarities in economic inequality

<quote>
Scientists Arnab Chatterjee and Bikas Chakrabarti from the Saha Institute of Nuclear Physics, along with Sitabhra Sinha of the Institute of Mathematical Sciences, both in India, have analyzed a variety models explaining different sets of data, and found striking similarities. The results show that the poorer majority of the population follows one distribution, while a small proportion of the wealthiest people veers off in a tail following a power-law distribution, in essence reflecting how “the rich get richer.”
</quote>

Small network phenomena?

"The savings/income distribution is normal/random until you reach the point where you have a significant number of people making their money work for them."

Does that about sum it up?

> "The savings/income distribution is normal/random until you reach the point where you have a significant number of people making their money work for them."

I can think of a few anecdotal cases where spending twice the amount on something yields more than two-times value. The $900/month my car costs me (according to edmunds.com TCO) is worth a lot more than 2x what a $450/mo car (the cheapest possible car) would cost me.

The more opportunities you have like this, the more wealth you gain even if you have the same spending habits as someone with half your income.

There's no doubt a sweet spot where every little increase in your wealth will lead to disproportionately larger gains in future wealth.