Great post. Where I Iive, most people are helpful to others, and nobody shouts about it, it is considered normal within this particular group of people, and sometimes extends to people outside the group. It does work the other way around, though: if someone, for instance, doesn't help a child that fell off his bike hard, he is considered an arsehole, and people advertising their helpfulness as something great are laughed at. I never really gave it much thought until you posted this. There's one thing I noticed though: people constantly and overtly helpful to far-away people in need in distant lands are often rather less helpful to those close to them. I don't know if that is a universal thing.
There's one thing I'm not sure of, though: you say that "there are no selfless acts". Even though I know all supposedly selfless acts can be explained from selfishness, I'm not sure that "there are no selfless acts" is a knowable fact, as it would require looking into the heads and finding the motivations of each and every person performing such an act.