This is from the Blizzard FAQ on the subject.. was cited elsewhere but:


Do our characters (my character and my recruit's character) have to be same level in order to receive triple experience?
No, but you must be within 4 levels of one another and meeting all other triple experiences requisites in order for both characters to receive triple experience. If this level requirement is not met, only the lower level character will receive the bonus.
For example: Should your character be 5 levels higher than your recruit, only your recruit's character will be eligible for triple experience (provided that all other requirements are met, as well).


Id love someone to go in and test it cause I am crying false too, but it is what the FAQ says.. If you are not within the level range then the lower level character should still be getting the triple XP, the higher will not.