Y'know, if they actually put some thought into those things, people might not hate them so much. It wouldn't take a rocket scientist to make some adjustable nylon spacers to brace them out from the spokes and actually put them close enough to the big cog that the chain can't wedge in between.

I just went and looked at the Huffy's steel disc; it's got a rib around it that puts it about 3/4 of a chain width away from the big cog, while the outer rolled edge sits against the spokes for strength. The Trek has plenty of room for the chain to drop off there, and none of the other bikes have surviving discs to check, but it's disturbing that Huffy got it right 30 years ago and nobody else seems to even try.