Spending 10's of thousands a month is getting up there, but "blowing through" more than $4k per month isn't necessarily an extravagant lifestyle. My guess would be that you don't live an as expensive a metro area as the author is basing his calculations on.
In a place like San Francisco, a few non-frivolous expenses can add up quickly:
- Your residence. A decent 2 bedroom place in a desirable part of San Francisco will run $3,000 per month in rent, a mortgage will be much higher. We're not talking anything extravagant here, just 600-900 sq ft.
- Travel. Paying for more than one person to travel to visit family/friends a few times a year can easily add up to $1,000 or more per month. We're not talking luxury vacations here, either -- just basic airfare (coach) and accommodations.
- Health expenses. As you earn more, you'll probably be more likely to spend more on optional health items. Things like LASIK for example. Also, as you get older, these expenses will get much larger.
- Kids. It doesn't even have to be private school we're talking about, but I imagine that clothing/feeding/entertaining more than one person adds up quickly.
- Any time/money trade-off. You have a limited amount of time and, similar to health expenses, you will be more likely to spend money to save time as you earn more. Each person's choices will be different here, but again, we're not talking luxury. Maybe paying for parking instead of a time intensive bus trip? Or arranging for laundry service? Or paying an unjust $40 bill that would otherwise take you 5 hours to fight?
Notice there's no talk of fancy cars, big screen TVs, luxury trips, large mansions, or extravagant dinners. I think this is the definition of "upper-middle class" that Tony is talking about. Nothing fancy, but a few things to make your life more convenient.