When I first began to study photography intensely over 8 years ago, my preferred image presentation was portrait orientation. I can't really explain why my eye preferred that orientation, I simply knew I had a bias toward the portrait orientation. Then I began to quickly learn about the powerful "near/far" composition where one can present a deep 3D image by presenting a very large depth of field spanning from a nearby rock or bush to the distant vista. Of course the Ansel Adams f64 group made this approach one of their cornerstones of image presentation. At that time, many images I was viewing were also in magazines where the preferred orientation is portrait.
During my first workshop with Alain Briot, one of the photographic exercises he emphasized was to capture an image with both a portrait as well as landscape orientation. Since that workshop I have made it a practice to do just that. At first I still preferred the portrait orientation, but recently I have noticed a significant change in my preference for landscape presentations. A significant majority, if not 100%, of the Smoky Mountain portfolio is going to be presented in landscape orientation. So i began to reflect on what might have led to the change in my bias.
The leading candidate is that the change in viewing devices has influenced my eye dramatically. The move from relatively square TVs and CRT monitors to the more elongated 16:9 HD TVs and LCD computer monitors has certainly influenced my eye's preference for landscape oriented images. Even the portrait oriented images I have now bother me just a touch when they are presented via my light box image viewer on the web pages. The only time I really like the presentation of the portrait images is when I flip my iPhone so that the image is presented in its full display.
Another factor is the relative newness of the "panoramic" presentation. I love this presentation and only web-based presentations on wide screen monitors or fine art prints can present the image as it is intended to be seen.
I don't know if this influence has made a major impact on all of photography, but it would certainly be interesting to study. My guess is that as we move away from magazine oriented photography to web-based photography, landscape presentations may become the preferred orientation for images. See if you can find any correlation to this hypothesis.