I don't think this is unique to Divine Intervention. As far as I know, anytime a card talks about the player with the most/least of something, it applies to both in case of a tie, rather than neither.
It's hard to say it in the card text though. "The player with the most holy cards in hand gets... or if both players have an equal number of holy cards then...", is obviously way too verbose. "The players with the most holy cards in hand..." is technically correct (and it's not totally unheard of to use a locution like that to mean "select all elements such that no other elements are greater than them"), but probably confusing to newbies.
Maybe it should go in the FAQ though.