Hmm...I'm also wondering if this was changed? From Blizzard Support Page:

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).
Will the experience bonus apply to only one character? Or are all characters linked to the account eligible to receive it?

All characters below level 60 on both the veteran and recruit account are eligible to receive the experience bonus.