UPDATE:
Just tried this again - and noticed something really weird. The behavior (of not displaying the art/details for the platform) only happens if the initial platform selected is the first platform on the list.
Example:
In my screenshots, I have 2 platforms - PS3 and Windows. If I load it up and BigBox starts off on PS3, the above issue happens. However, if I select "remember last platform" and I exit BigBox while I am on Windows, then when I come back to BigBox later, it will start off on Windows - and the image + details for Windows will be displayed.
This suggests to me that there might be some flaw in the XAML for the platform view - if the first platform alphabetically is the "starting" platform, BigBox fails to display this additional data until the user moves through the selections. However, if the "starting" platform is somewhere lower in the list, then BigBox displays as intended.
I also tried to reproduce this in the Default theme - does not happen there.