It's not about physical resemblance so much as shared anatomy. For example, while a human looks nothing like a kiwi and evolving half a world away, they're both bilaterally symmetrical, have four limbs (even if the kiwi's fore limbs aren't immediately obvious), two eyes, a cranium and a vertebra. All these features are there because of shared ancestry that is much closer in evolutionary terms than say, a starfish. Even a Shark has most of those features in common, again, because of shared ancestry.
How about some of these completely terrestrial creatures that all evolved right alongside humans? Let's see, there's the leafy seadragon
, the hagfish
, just about any species of octopus
, most mult-eyed multi-armed insects
, and tons of others.
Sure, you can claim a starfish is similar to humans, but you'd be about as wrong as you are about the na'vi and the rest of Pandora, mostly because any
evidence you have is superficial and based solely on what you see on the screen. No dissections. No detailed scientific journals. Just a few pictures of them running around, about as accurate as looking at a human right next to the aforementioned starfish (or any of the examples above).
In other words, the na'vi are clearly the freaks of Pandora, and they probably do
share those treats but, for whatever reason, they evolved away from them and they became recessive, redundant, or simply concealed in some fashion.
You know, kind of like our tails. Or most of our fur.