First, Fix Your Skull

They seem to be forgetting one item. Air conduction is much more sensitive than bone conduction. Only if the conductive mechanism of the middle ear is damaged does bone conduction have any significance. The volume and shape of the ear canal is likely to have more of an effect on normal hearing than any change in the shape or size of the skull. It would be interesting to run a similar study on a group of people with advancing otosclerosis a disease where the bones of the middle ear become frozen and can not transfer vibration from the tympanic membrane to the inner ear. Variations in hearing between people with normal hearing is to the greatest extent due to the interpretation of that thing between the ears. 

I've posted more than once about how different ears hear differently. If your ears stick out from your head, you will hear much different from someone with closer to the head ears. This is why there is disagreement among people about what sounds "good." I suppose the physical dimensions of your skull contribute to this factor since ears are attached to the skull, but since you hear with your ears, not your skull, I have no opinion on skulls.

If your ears stick out from your head, you will hear much different from someone with closer to the head ears. This is why there is disagreement among people about what sounds "good."

Well, it's one reason among many and not likely to be the greatest one. 

No doubt about it. Size of ears is likely relevant, as well as actual acuity. Just as some people can see better than others (some folks don't wear glasses) some people can hear better than others, "better" in the sense of being able to discern a greater frequency range. Human hearing and vision are both very limited when you consider how great the range of light wavelengths and sound frequency spectrum are. We just don't see or hear what we're missing.