Reason for Aerial Assault on Tantalus/Reaper?

Since 6th edition fast vehicles can move cruising speed and still fire two weapons using full BS, is there a reason for the Tantalus and Reaper to have the Aerial Assault rule?

I know most people consider the Aerial Assault rule to not ignore the effects of Hard to Hit, but what about ignoring crew shaken?

There is no reason for it in 6th ed.

Just hasn't been updated from 5th ed.