Lower level monsters had thier damage decreased on natural attacks, but monsters that had access to manufactured weapons did not see the same drop. Shame the loss of the devastation of the minotaur horn charge.
Natural attacks generally do less than manufactured weapon so don't automatically discount the possibility of Players trying a disarm attempt.
Indeed, 3e minotaurs' horns were a very devious trap. The horn charge ability encouraged players to close to the minotaur allowing it to get off it's full attack routine, and possibly an AoO too.
And since the minotaur is the first base critter to get multiple BAB attacks, it can be a rude awakening. Especially for a player trying to give the minotaur a taste of its own medicine by charging it first.
AoO with great axe +9. "Hi!" great axe +9 "How are you doing?" Horns +4 "I'm doing fine" great axe +4 "Good-bye!"