Yup, that's true; the standard headers need not be actual files, so there may not be an actual path to them. The underlying principle remains the same, however; <> goes right to the standard include "files" (whether or not they're actual files), while "" checks files in (actually, relative to) the the current directory before checking the standard ones (which, again, may not be true files).
To get really technical, there's nothing that says the "" form has to search the current directory (since theoretically, there may not even be such a thing as a directory on every platform), but in practice, that's where it usually looks.