The difference, vfrflyer, is in the application of the two regulations:
Schedule 8 is cited by Art 22(1)(a) and pertains to licences issued by the CAA. It has no other purpose. A foreign licence is accepted by Art 21 (3) or (4) quite independently of Schedule 8.
By contrast, Rule 22 of the rules of the air, prohibiting VFR at night, and the rest of the Rules of the Air, get their force from Art 84, and apply to all aircraft flying in the UK, regardless of their nationality.