Derek,
To be fair - nearly every question on this survey is generalized, and the atheism/theism/other question is no different. Lumping together monotheistic conceptions of God under the title "theist" makes sense to me - each believes in an omniscient, omnipotent, and omnibenevolent single being - whether or not the remainder of the respective religious window dressing is the same is beside the point. This is a survey that asks very general questions - the more specified the questions, the less significant the data will be. Suppose the question supplied an option for each of the world's 22 "major" religions - Would any of the options exceed 5%? What kind of inferences could be drawn from a question formed such that it would satisfy your above complaints?

This debate could be had about any of the questions on this survey.

My guess is that specialists in the Philosophy of Religion had major difficulties with this question - While "theism" seems to be relatively well-defined, what about the agnostic-atheist distinction? I really have no idea where to classify, say, Hinduism on this scale.

That said, I think nit-picking the question misses some very interesting results, particularly with respect to the specialist differences. My guess is that a larger number of the general public would identify themselves as theists than the %14-18 of all philosophers who identify themselves as theists. What is interesting, is that %60-70 of specialists in PR consider themselves theist - I suspect that is a much larger number than the general public would report. Would any of the other questions show such a strange trend between the general public, philosophers, and specialists?