I've lived on 100K or less most of my life, with kids, and we've been very happy. That's kind of the argument here ... what does it mean to be "comfortable"? I've been happy, as are my kids, so isn't that comfortable? We've always had enough saved to cover crises. We've had fun vacations. The kids have had fun activities. So I ride a bike instead of an extra car payment ... so what? We're happy.
And yes, it does vary place to place. Utah is actually pretty average to above average with cost of living. Other places would be better. Somewhere like the Bay Area would be much more difficult of course.