From what I remember in the one YEA! camp I went to many years ago, they pretty much made a case for the right foot being more natural...
Such as in drumset playing, the backbeat rhythm has the right placing notes on the first and third beats, rather than the second and third.
This is what I've always heard as well, just a more natural way. Also since most people are right handed (no offense to the lefties out there) it's more natural to lead with the right foot. Line up a group of "non-marching" people and ask them to take 3 steps forward. The majority will lead off with their right foot. Another point in the "more natural" philosophy; what hand to do
most drummers
usually start playing with?
That and Cadets have always liked to zag when others will zig.