The problem with animals that are different in any way is that scientists can't even agree on why that's the case. For example, the plumage of a peacock. What's with the "eyes" and why such a big ass tail when other bird species still manage to get laid without it. Or why did Platybelodons have to be the only elephant with a giant duck-billed mouth like that? Paleontologists don't have a clue, not a friggin' clue. So, when the experts can't bring even their extensive experience to bare on a subject like that, it's hard to plausibly do so, myself. But it does seem as though Human intelligence shaped our own body plan from something obviously very animalistic to something more aesthetically agreeable, shall we say.
Big, boney brows over the eyes, excessive hairiness and hunched over gates were gradually given over to much smoother, streamlined features and I have to believe that part of the reason was due to our ancestors not digging the animalistic look, anymore. I can't imagine an alien species wishing to retain its primitive traits anymore than we did. Even now, consider someone who's got a low forehead, how unattractive that can be. And why? Because it's sort of a primitive trait that's no longer favoured. So, when I see these examples of aliens that look like something George Lucas farted out, it doesn't ring true.
