The adoption of the Rugby Football Union code with an exception is significant. Even at this early stage the rules of the game were the rules of the four Ivy League schools making up the Intercollegiate Football Association. From the very start, the Ivy schools were determined to make their own rules making changes as they saw fit.
In a few short years, Yale graduate Walter Camp had modified the rules in such a way that American football was it's own game; different than the code of Rugby Football Union. Rugby Football would remain on the college campuses but to a much lesser significance to the popular American game which we now simply refer to as football.
These days, rugby at the eight Ivy League schools follow the rules of the International Rugby Board (IRB) and USA Rugby.