The Unbearable Lightness of Being Alien

I always bugs me how nearly all aliens in movies, litterature and TV obviously evolved on Earth, left  the planet ages ago, forgot all about it, turned purple, only to return and try to recapture it?
Of course I know that it's about emotions and understanding and seeing ourselves from the outside, but wouldn't it be great if just once in a while something alien - truely alien - turned up?

All aliens seems to have evolved from the exact same branch of vertebrae - mamals - with spine, skull, jaws, arms, legs fingers and toes. They're all very monkeylike. Even those with scales and wings. And this just doesn't add up or make sense.

Nom, nom, nom...

Features:
So lets just talk about the jaw for example:
All aliens have jaws. And they're full of humanlike teeth. 
The vertebrate jaw usually bears numerous teeth and probably originally evolved in the Silurian period. The jaw evolved from the most anterior two gill arches supporting the gills and appeared in the Placoderm fish. This further diversified in the Devonian. The two most anterior arches are thought to have become the jaw itself and the hyoid arch, respectively. So getting yourself a set of gills-turned-into-jaws, and then adding white teeth and fleshy lips on top of them, seems to be the hippest thing since... I don't know.. five fingers? If you want to know more about jaws, there is a neat Discovery documentary about it here.

Of all the animals here on earth it's only vertebrates, that's got this feature and a little googling has made it clear that even though species like fish (including lampreys), amphibians, reptiles, birds, and mammals are vertebrates, more than 95 percent of known animal species on earth are in-vertebrates.
So how come that 95 percent of all alien lifeforms are vertebrates? 
And how about that spine, eh?

How come almost no designers or worldcreators thinks about where and what their beings are coming from? And how a different evolution on a very different planet would affect life. The only way mamals could be on top of things here on Earth is because the dinosaurs died out 65 mio years ago, and left the place to us! 

99.9 % of Star Trek aliens differ from humans so little that you start wonder why they bother putting on the make up at all. I'd love to see aliens being... well, alien for a change. Not even like THE Alien, but alien as in uncomfortably strange.

One of the few TV-programs I find interesting in this way - and inspired me quite a deal - was the Discovery Channels docufiction Alien Planet.  The show uses computer-generated imagery, which is interspersed with interviews from such notables as Stephen Hawking, George Lucas, Michio Kaku and many more. Wayne Douglas Barlowe (Illustrator and Head designer on Avatar and more) has done most (if not all) of the designs of the alien creatures together with the 3D animators, scientists and zoologist, that's contributed to the making of the show. Alien Planet was filmed in Iceland and Mono Lake in California and it's so worth watching. Just remember: It's a docu-fiction, so remember it's not science fact, just imagination. 

I sometimes wonder if aliens - if we ever meet any - have more in common with the oddness and unfamiliarity of the designs of HP Lovecraft than those of George Lucas.