That number, in its defense, does cover 95% of workable wage saving scenarios.
I consider myself mustachian, so does my spouse (my kid is 2 months old so she doesn't get a say yet). My wife is a stay-at-home mom for the forseeable future, and with mortgage+HOA for a 2-bedroom condo, and family health insurance that allows us to see a pediatrician on a proper schedule, we are over 50% of my take-home income, which is far from low even for Southern California. No, we don't have car payments, and yes, we save... but we could not realistically break that calculator even if we tried.