The angel stereotype comes with the "volunteer" type person I think. It's like the stereotype of the "hot nurse" will always be a hot woman and people will rarely think of a hot guy or something.

I was just reading this and from http://en.wikipedia.org/wiki/Nurse_stereotypes

"The image of a nurse as an "angel of mercy"—selfless, altruistic reliever of suffering—is based on the origin of nursing in the religious orders. In modern times, Florence Nightingale was the epitome of the nurse as an angel.

However, angels can fall from grace. Nurses such as Beverley Allitt or Kristen Gilbert, who have deliberately killed patients under their care, have frequently been referred to as "angels of death"."

I totally forgot abou the angels of death. That's not good. Not good at all.