I've read a few posts lamenting Devastator walking on all-fours. I think it's brilliant. Something that weighs as much as Devastator would easily require as much surface contact as possible to be stable-- three points of contact makes sense. Two-legged, he'd be very wobbly, and one sand shift would put him down. We humans weigh nothing by comparison, and walking in fine sand is still a challenge. Then there's the cinematic reason: we want to be able to see him! If Devy's head is 300 feet in the air, all we'll see most of the time would be his feet. To zoom out enough to see all of him would mean everything else in the shot reduced to specks. It's much scarier to have his head, four stomping feet, and that huge mouth right down in the action!