That is exactly right, well at least according to the Alien comics. The Xenomorph takes on characteristics of the host. Hence why the first aliens (from human hosts), bear a striking resemblance to the human form. And why the alien that took the dog in Aliens 3 looked more like a dog.
If you remember the action figure line from a while back, this explains why there was a bull alien, a snake alien, and a couple of other species. The host species contributes some of the genetic makeup of the new alien.
To a certain extent. The presure exserted(sp) by the facehugger limbs is optimized for a humanoid host. Thats why the dog was horribly scarred. There would be never a Snake Xenomorph simply because, unless we are talking about an anaconda, the host would be too small for the face hugger.
We have to take anatomy and size into consideration. A small host would never provide enough food for the embryo to mature.