Just guessing here, but if you read @todd-weaver’s latest blog post, it says ‘‘Aspen (black case)’’,
so it could be that the casing were to change in later revisions 
Or, if you look at the 2 img with the PCB front and back, would that imply that they plan to switch the CPU to the back, closer to the metal display chassis?
Pics are here:
Interesting…