I was told last week by a research audiologist that lip reading is far more prevalent in the hearing population than we would expect, to the point that it is questionable whether deaf individuals are really any better at it than hearing individuals. Instead, apparently we're simply more comfortable relying on lip reading. I'm still somewhat skeptical of this - the McGurk Effect notwithstanding, I think I communicate far better with just a visual signal than most hearing people can. Still, I suppose the argument that it's just a different set of communicative strategies can't be immediately dismissed; we see similar phenomena in spoken language, in that two second-language speakers may perform similarly in a classroom environment, yet be perceived (and perceive themselves) as having widely varying abilities in a real world situation.

The theory would go, then, that those of us who are fluent lip readers (if you'll pardon the misuse of the word 'fluent') aren't necessarily picking up more phonemes than anyone else; our apparent superior abilities are simply the result of lots of practice at relying on contextual analysis, pragmatics, and the "Smile and Nod" method (which actually can have the paradoxical effect of reducing isolation in social situations ... though I suppose that's a topic for another time). Speakers for whom lip reading is a secondary channel aren't used to relying on these strategies, and furthermore may feel uncomfortable, realizing that their access to language is very different than it usually is. However, they will prioritize visual stimuli more heavily when auditory stimuli are unreliable (say, in a high-noise environment).

Between my conversation with the audiologist mentioned above, and the Googling I just did, it looks like a lot of this research is being done at the Royal Institute of Technology in Sweden. I haven't found the specific paper(s) I was looking for - the ones that try to find a correlation between lip reading abilities and some more fundamental trait - but there's some interesting stuff out there.