Animated films are NOT "obviously" voice-only.  Many modern animated films use motion-capture technology to capture information on an actor's movements/mannerisms.  In these instances it could be argued that someone is not voice-only.  Then there's the more complicated situation of rotoscoping, where it has to be argued that although it's animated, the actor certainly has contributed more than simply their voice (they actually give a full performance, which is then relayed to us in its entirety).

For those who think it should only be for animated films, I'd also suggest that "voice-only" has a place in movies such as Pan's Labyrinth (where Pan has one person as the character Pan, and another doing the voice), or in Woodenhead where the voices are supplied separately from the actor's performance (and by other people).  Then there's the obvious case of narration (narrators may be credited as something less obvious).

As always with these things, what seems to be a given certainty actually has numerous exceptions.