Royal birth is an element of heroism because many royal houses (families) are who they are due to the valorous deeds of one or more members of their ancestry. These family members either a) fought  b) conquered  c) seized, or d) dethroned someone else for their own gain.  In ancient times this was not seen as "politically incorrect" but actually as a sign of inner courage, power, and strength. Many kingdoms, to this day, are disputed as to how some of their kings or queens gained power. One thing is for sure: The power is often always gained by very heroic and extraordinary battles.

Most current royal families come from a history of wars, seized crowns, betraying conspirators, and loads of lands and money. The English court can boast the 7 years war, the 100 years war, the Wars of the Roses, 1066 Hastings, and tons more.  The Spanish court can claim the exile of the Arabs from Spain, the Armada, the Spanish American War, and tons others more. The Romanovs, the Hapsburgs, the Battenbergs, all those royal families have endured harsh wars to either protect or obtain land and power. This is probably why this is seen as an element of heroism.