Originally Posted by cmbs
I see. Maybe some older readers can't handle the cover image?
I don't think it's that so much as the fact they're now using a better MobiPocket creation tool.
Baen are much the same; their older Mobi books with a ".prc" extension are rather primitive and lack navigation links, etc. Their more modern Mobi books (with a ".mobi" extension) have proper cover images, working nav links, etc.