Well, as OCR points out even Highland Games within the U.S. are different.
- In the Southwest where I live, you will not see as much brigadoonery because it's too warm (or hot) and humid.

I have been to only 2 Highland games in Scotland, so my experience is limited:
- In the U.S., the focus is still the games, but what seems to draw the crowds is the pipe band and solo competitions that are conducted also during the athletics. These competitions are mostly sanctioned by the U.S. Pipe Band Association (EUSPBA) and the Western version (WUSPBA), who approve the judges and maintain a roster of grade levels for the pipers and bands. Also, there are Highland dance competitions (primarily with young ladies competing), but I don't know anything about their organizational structure.
- In Scotland, there may be a clan host for an athletic event, if it is held in a particular clan territory.
- In the U.S., there will be a clan gathering of as few as 6 and as many as 76 clan associations, their purpose being to hawk memberships and provide shade to existing members. These gatherings can feature: torchlight ceremonies in the evening, tug of war competitions; bonniest knees contests, etc...
- I was surprised to see hamburgers sold at the Highland games in Scotland. At the Taynuilt Highland Games, there were 3 different vendors selling burgers, including a church that buttered the buns. To be fair, I considered it important to sample a burger from each, and 2 of the 3 were quite good and American-like.
- NO brigadoonery in Scotland, but I did see period-people wearing large bonnets and the great kilt at the Taynuilt games - these were not Americans, Jock Scot.
- The period-people in some states in the U.S. can get away with wearing dirks and swords even if it is illegal to wear such blades, because of the circumstances, but are required to be "peace-tied" in their scabbards. I saw no period-people with swords, and I don't recall dirks.
- In the U.S., you see plenty of vendors selling kilts, books, knick-knacks, anything of a Scottish or Celtic flavor. No such thing did I see at the HG in Scotland.
- In the U.S., there are usually 2 or 3 musical groups to perform. I saw nothing of this at the HG in Scotland.

That's my quick-and-dirty list of similarities and differences. To work for me now!