in real life voice and appearance don't have to match, but usually in fiction they do because they would sound strange otherwise..that's why when dubbing batman you don't cast some guy with a squeaky voice but you want him to be low tone and imposing, regardless of quality of acting.
same happened here
Might be a possibility. Yet I just fail to see a problem if Samus has had a sexy voice. Of course if the case being that the sexyness of the voice being forced making the voice acting being bad, that could be really bad.