Jun's comments on the spine are important. Doing a tumbling roll has a purpose-the completion of a different kind of maneuver. It exposes the entire length of the spine to potential trauma by rolling on it. The 3/4 aikido roll exposes the spine to one pass with the ground. Everything else is dissipated over soft tissue. The flying breakfall (tobu ukemi) if done properly should not require twisting mid air and as pointed out by Greg is an extension of the front roll-just a higher start point.
Personally, I cannot see a gymnast taking a high speed roll on a hard surface without a lot of pain. Whereas, an aikido roll should minimize any pain and trauma to the spine.