Cameron did shoot Avatar in 16:9, and the theatrical release included 16:9 and 2.35:1 (cropped), depending on the theater. And Imax is around 1.4:1 with a huge screen that fills the entire field of view, both horizontally and vertically. In a related argument, theater consultant Anthony Grimani advocates "constant area" rather than "constant height" image reproduction, which means that narrower aspect ratios should be taller than wider ones. Of course, this is only practical for front projection systems with 4-way masking screens.
On the other hand, I've also heard knowledgeable people say that the human visual system is more sensitive to horizontal resolution than vertical. Also, Cameron and many other directors say they really like the compositional possibilities of 2.35:1.
BTW, "immersive" is not included at merriam-webster.com, but it is included at dictionary.reference.com, and it's included in the Oxford English Dictionary. Therefore, it's a real word in my book.







