ray_afraid said:

I'm interested to see what role the speeder-bikes were originally meant to play in the sail barge scene. I've always had a suspicion that they were designed for that scene as the fins on the front and overall shape/design and color looks like Jabbas sail barge and skiffs. Now that BTS photos of them at the sail barge shoot have emerged, I'm more convinced than ever.

I always thought the explanation for their presence was simply that all the ROTJ stuff was in trailers, and all the trailer came to the shoto.