Actually I consider the way the Na'Vi launch there bow very practicle. It's nothing odd.
The 15,000 years or so of human experience in the use of the bow tells otherwise. This is not to say that the Na'vi release is not possible or practical, but for humans at least, it can be safely said to not be the best. The proof for this is simple - over the span of human existence the inverted-hand draw has never (to my knowledge) been widely adopted by any culture. Given that humans are quite eager to explore more efficient means of killing, if it worked better to loose one's string that way, we can be assured it would have been.
Instead, we have variants upon the Mediterranean release principally in the Western hemisphere and the Turkic/Mongolian/thumb release in the East, though both styles turn up throughout the world, generally dependent on the use of the bow. Thumb releases are common among horse archers, as they permit the arrow to be lain on the outside of the bow, negating the need to run the arrow between stave and string when nocking (faster, easier to do while riding).
Also you can see when Jake is learning how to probably use the bow, they're shooting the bow differently than, at least I am, used to be. They're not loading an arrow, taking aim, pull the string and shoot. It's more like they got an arrow ready, raise the bow while pulling the string and THEN they aim.
This is for at least two reasons. Firstly, their style is based upon Japanese Kyūdō, which is often practiced in a very ritualized fashion, sometimes with a spiritual purpose or goal. It has very distinct phases of motion and rigourous movements, many of which are unique to Kyūdō. Secondly, it is being performed by actors, for a film. They have thus taken an already stylized form and further stylized it. They are not, in fact, practicing archery, but conveying a vision of it. They do this very effectively, and I do not mean this negatively in any way, but it is important to distinguish between the reality and the fantasy.
As far as aiming - instinctive archers, and I would count Kyūdō practitioners and the Na'vi among them, do not "aim," per-se. They instead focus intently on the target (often upon a specific point on the target, even down to a single hair), and through much practice, are able to place the arrow there. Think of throwing a ball. You do not "aim" the ball, your body simply knows how to get it where you want it after many years of learned motion.
Did you noticed that Na'Vi rarely carry more than 3 Arrows? They have to fire with high accuracy.
Given the size of the arrow, carrying more would be impractical. Also, when hunting, one generally does not get off a second shot if the first misses, so more than two or three is not needed
I'd be interested to see that. We need the DVD so we can get some screencaps showing the Na'vi arrows, to compare thier arrow designs to 'real rainforest native' designs.
I screen-capped that image of Neytiri from the trailer. And below I have attached a photo of the Peruvian arrows I mentioned. They are, I believe, are from the Yine tribe, and I acquired them while in the Manu basin. According to CineFex issue #120, WETA "knew from the original concept illustrations that there were not going to be a lot of feathers on their creatures... so had to find something else with which to fletch the Na'vi arrows, [and] drawing on Pandoran plant life we'd seen in the artist's paintings... created highly believeable pieces of organic matter that could have, in theory, come from Pandora."
From top to bottom:Two arrows for large game
Fletched end typical of all arrows shown (there is no nock)
Two arrows for large game (barbed)
An arrow for birds
An arrow for birds or fish
Overall sizes are around 60-65 inches (152-165 cm) in length.I also have two Yine bows, which are of D-section and probably around 30-35 lbs. draw.