What you are referring to is what the Wall Street Journal once called the "HENRYs" - High Earner, Not Rich Yet. Or in other words, "once I spend all of my money, I have nothing left!".
This is an argument that can be made at virtually any income level. Consider the following article and this really charming infographic they put together:
http://www.wsj.com/articles/six-figure-incomesand-facing-fin...
http://si.wsj.net/public/resources/images/BF-AE118B_05WIc_G_...
(infographic from http://www.wsj.com/articles/SB100014241278873236896045782201...)
After all - $400k isn't really that much, after you've paid taxes and put away $22k per year for retirement and the kids' college, and after you're done spending $87k per year on a mortgage, $25k per year on property taxes, $40k per year on maintenance and utilities, $30k per year on groceries, $21k per year on dining out, $26k per year on vacations, $24k per year on car expenses, $12k on country club dues, $10k per year on children's sports, and $9k per year on gifts and donations. Why in fact you're $10k in the hole!
I don't quite know how to say this other than bluntly, but $125k is a long ways above median household income everywhere in the country. For comparison, the median household income for New York City is $50,711 and the median household income for the San Francisco Metro Area is $83,222. Most people live off less than $125k, don't pretend it's impossible. Expenses tend to find a way to encompass available income unless you make a deliberate effort to stop that - even for people making $400k per year.
$125k isn't "rich" in the sense that you could quit working and live off the income from your investments or commute every weekend from your villa in the Caribbean, but it's vastly more than most people will ever see, and it's enough to be totally financially secure _if you choose to be_.
This is really the distinction the article is getting at: some people use "lower/middle/upper" in the sense of income quantiles, other people use it in the sense of working-vs-rentier classes (i.e. proletariat-vs-bourgeois). But there's always been a group of HENRYs - Marx labelled them as the "petit bourgeois".