Proposed resolution:

Strike the parenthetical note from the Effects clause in each of the paragraphs mentioned above.

[ifstream.cons], p2, [ofstream.cons], p2, and [fstream.cons], p2 say about the effects of each constructor:

... If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure).

The parenthetical note doesn't apply since the ctors cannot throw an exception due to the requirement in [basic.ios.cons], p3 that exceptions() be initialized to ios_base::goodbit.