Really? In the U.S.? Case study? Without kids and if you don't really spend any money on recreation or vacations (before or after retirement), maybe. Or if you somehow have a job that will give you a pension (with health insurance?) at 50, sure!
Assume someone making $50k lives in not NYC, I imagine this scenario could be a lot better.
For a more extreme version of MMM, read http://earlyretirementextreme.com/. This guy (Jacob, who MMM mentioned in this interview) never earned much money (never over $50k prior to becoming financially independent), and retired after working 5 years. With a little creativity, most people can retire far sooner than standard retirement age.
Assuming a $50k income post-tax
And there are methods to pull this money out well before the standard ages without penalty, such as Substantially Equal Periodic Payments (SEPP).