I would be very careful trying to reason by analogy there.  ==, is, and javascripts === are rather different in detail, from what I understand.  Nor do I see what javascript has to do with this issue :)

As far as the remaining documentation issue here, IMO to follow the convention used most often in the docs (and docstrings), the text in Chris' example should read:

   If *allow_nan* is true

That is, drop the code markup and capitalization to indicate that any true value is accepted.  A naive user will use True, a non-naive user will understand the implication.  I know Ezio doesn't think this is worthwhile, but I disagree :)