Hi All, I saw this and I thought i'll put in my part as it is an good thread.
As I understand by An historian Halloween was from "All hallow eve" and yes Halloween become a fun event in the us, but when Halloween came back to the uk, it became a Horror by the christan, so they change there ways by calling their events as "All soul day" and/or "All St. day". Back in the Medieval times it was called "All Hallow Eve" this also go's for Samhain. All these events are base on/around Samhain which dates back in the Iron and Bronze age.
So you cannot blame for the us to call Samhain as Halloween; As America wasn't known until the 1600s-1700s by the English.
When I'm with 'what I call' everyday people I call Samhain as All hallow's eve but in my mind I see the word of Samhain. People seems to understand All hallow's eve and they do not mind you saying it.
Best Regards & Blessing!