Negative object/data property assertions in EL++

I see that negative object/data property assertions are explicitly 
disallowed in the EL++ fragment. But one can express

NegativeObjectPropertyAssertion(p a b)

as

DisjointClasses(ObjectOneOf(a) ObjectHasValue(p b))

which is allowed in EL++. Same is possible for data property assertions 
using DataHasValue restriction. So I'm wondering if disallowing negative 
property assertions in EL++ is necessary.

Regards,
Evren

PS: I've added a review comment in the fragments document regarding this.