Well, not sure if the original poster of this thread is still on-board, but I found out what the issue with Kindle Previewer is. I am having trouble rendering "Kindle" and "Kindle DX" cover images using the Kindle Previewer on my laptop (Windows XP). Well, for fun, I installed the KP on my wife's laptop (Windows 7), and lo and behold, the cover images render perfectly for "Kindle" and "Kindle DX" devices.
There has got to be a bug with any XP-code graphics rendering, or something else funky going on with KP. By the way, I provided Cover Image on this final test via Calibre, which was the original way I desired to due it (yes, I like the GUI better than the command-line stuff).............