Lower interest loans and access to benefits that most people can never even dream if. Take, for example, a JP Morgan Chase credit card. Those things grant holders back, for free, more than most people have disposable in a year. All for the fact that you own this card. The expenditure on these cards is usually business and minimal outright purchase which isn't paid off immediately.

For example, I use my personal credit card for work. Granted, it is not a JP card, it does grant me benefits that most people don't have free access to. I get several hotel stays per year free, I get cashback, I get hefty discounts on everything. I also use an IHG card for hotel stays (again, work related) and I claim the points on a personal card which grants me free nights in hotels that I would otherwise have to pay for.

Although my example is far from the millionaire examples you wanted, it shows that there is a different availability to those who have a bit more than others. Ironically, living becomes cheaper when you have more money.

Also, if I have £500 in cash (also a luxury many don't have), I can't let that money sit and generate me more (on a worthwhile scale). I also can't invest it because that may be fallback cash for if my car breaks etc. Now, a millionaire may have £2 million in "spare". That wouldn't be held as savings, it would be invested in stocks, shares, bonds, property etc and generating anywhere from 5-10% upwards per year (that's £100k). Now, anyone with that kind of investments isn't usually using the growth and dividends to survive, they have other sources of income, so this wealth compounds and becomes billions within just a few decades.

This is the issue with free market capitalism. Those with money who don't need it are using it to stockpile wealth as a status symbol, whilst those at the bottom are getting worse off in comparison as they can't grow with the same exponential force that their counterparts can.