As has been stated...modern, computer controlled cars will run ok, without damage, on lower grade of gasoline. However, higher octane prevents pre-ignition in high-compression engines. The on-board computer will detect pre-ignition (what we called "pinging" in the old days) and adjust timing, etc. to prevent it. Thus no engine damage. However, the changes to engine settings will change performance, including fuel economy. Thus, using regular in engines designed for premium is, in most cases, false economy. Cost/gallon less, but, miles/gallon less also.
So, everyone is right. You CAN run regular engine in a GLE without damage. But you probably aren't saving much money on fuel.