There might be more experts than you'd think. On another forum, there is an user who essentially knows the C++ standard by heart. And as far as I know, he is neither part of the C++ standard committee nor is he working for a C++ compiler vendor.
I would expect to find many more people such as him in these two groups.
Even so, one doesn't have to know everything about a subject to get away with calling oneself an expert these days - [i]far[/i] from it, in fact (unfortunately).