I think that's basically what's called institutionalized sexism, in that it's not so much that the person doing it is overtly sexist, but they're responding to the norms of society, which in this case is "heroes are male, love interests/helpers are female".
I tend to think part of the reason this is coming up now is because Wall-E is about robots-- did they really NEED to sexualize (okay, genderize) robots? I mean, why did Pixar feel that need in the first place?