Dicho,

The origin of the "dropped H" is from a time when French pronounciation was the fashion (as in Honour, hour, heir), this later changed when the fashion changed to more "Germanic"(hard H) pronounciation gained favour (however, there are throw backs as in the, slightly archaic, usage "an historian" and "an hundred").
What I cannot understand is why the Americans insit on the hard "H" on everything EXCEPT the word "herb".
It has been argued that the "dropped h" in "working class usage" started not as lazyness, but merely as an inability to change with fashion (I don't buy that myself, but, as they say, "you pays your money...").

Walrus