Para rematar el tema y corroborar lo dicho por Woodspoon, aqui copio unas palabaras sacadas de la web digitalbits.com:

Also today, we've checked with the studio and have learned that James Cameron's Avatar will be presented on Blu-ray in the 1.78:1 aspect ratio, with DTS-HD MA 5.1 audio. Run time is 162 minutes, which appears to be the theatrical cut. Now, before anyone gets their panties in a bunch that it's 1.78 and not 2.35... our information is that the 1.78 ratio is the preference of Cameron. In his mind, the IMAX presentation is the preferred theatrical ratio - not the 2.35 ratio seen in traditional theatres. By using 1.78, all of that original IMAX presentation image area can be presented. So essentially, you're not losing anything in the image by having it 1.78 vs. 2.35... you're actually gaining more image. So that's the deal. The DVD and Blu-ray are NOW AVAILABLE for pre-order on Amazon.com.

Como dice Woodspoon, se confirma que el 1.78 es el formato preferido de Cameron y que ganamos en imagen por arriba y abajo. Lo cual confirma que el 2:35 esta sacado del 1:78.
Posiblemente nunca se comercialize Avatar en 2.35.

Asunto zanjado para siempre