When someone is hanging out of a window to escape smoke and heat from a fire, I highly doubt that the first thing they ask their rescuer when they climb to ladder to get them would be "are you a Springfield resident or live within the 15 mile limit? If not, please get some who is to save me...

That's not the point. Ordinances (law) are enacted for a reason. In this instance, probably for emergency callback purposes. If the city doesn't enforce this law, what others are they not enforcing, or won't enforce? Not enforcing laws, codes, or ordinances, leaves the city liable should something untoward occur.

Is the federal government just as liable for not enforcing laws?

It may also be a case of keeping payroll (tax) dollars local, and keeping the employee "vested" in the community. I've heard both espoused as reasons for a residency requirement.

If you really think that politicians are worrying about callbacks when they enact residency requirements, I have a beautiful bridge to sell you in Brooklynn.