In a system like Apple's iOS, it takes the application programmer a lot of effort to decide on what the landscape and what the portrait layouts will look like - can include resizing and repositioning of each field of data, which is very tedious.
Since the car's software is designed to only show in landscape, I strongly suspect if the screen was rotated 90 degrees, the content would rotate 90 degrees as well - it isn't magically going to re-orientate, I am pretty sure.
I know the 'old' S had a portrait screen, but I don't think that is a generic rotation function - it is model/screen specific.