I did a blog post way back in 2005 about the reason why kilts are typically made today with three straps, rather than two, and arguing for the practicality of two straps.
http://kiltmaker.blogspot.com/2005/0...lt-straps.html

It's not a "North American" thing, but a fashion born and bred in Scotland I am afraid! For the record, all of my kilts have two straps!
M