Well, Donner was a classic journeyman director - not someone who necessarily felt he need to put an auteur-style stamp on all his films by making deep personal statements (like a Stanley Kubrick, David Lean, Tim Burton, or Woody Allen), but a consummate professional who could nonetheless turn out great work. Hence the eclecticism.

Other examples: Michael Curtiz (Casablanca and The Adventures of Robin Hood are both great films, but you'd have to be psychic to spot any auteur-style link between the two if you didn't know who directed them). Robert Wise (The Haunting followed by The Sound of Music and later The Andromeda Strain - again, I doubt anyone would guess it was the same director just by watching the films).