This Isn't New
This rule isnt new. Look at the following animals from the MM: lion, crocodile, and elephant. The lion's (Str 21) claw attacks only have a +5 damage modifier. Either of the crocodile's (Str 19) single attack routine attacks, bite or tail slap, have a + 6 damage modifier. The elephant (Str 30) has two alternate attack routines, either slam/stamp/stamp or gore. The slam has a +10 damage mod and the gore a +15. If a natural weapon is the only weapon in an attack routine, it is by default a "two-handed" weapon as far as damage modifiers.
EDIT: Also, the converse of that last sentence is true. A natural weapon is a "two-handed" weapon as far as damage modifiers if and only if it is the only weapon in an attack routine. This rules out a lion making a single claw attack for 1.5 damage.