Well, there are alternative ways to reduce the risks presented by a fire in the primary staircase trapping people inside.

For example, good sprinkler coverage of the primary staircase, strict rules prohibiting storing anything flammable below the staircase or running electrical wiring there, compartmentation so there's time for the fire brigade to arrive before a fire can spread between homes, housing options for vulnerable citizens so only able-bodied people have to evacuate via the stairs, and so on.

Of course, many American buildings are made of wood, so it's understandable why American fire codes look different to European ones - and if I had to be in a burning building but could choose the design, an American-style single storey suburban home where every room has a window you can climb out of at ground floor level is hard to beat!