[rashkae]

Have you been updating Kindle for PC? I forget what version the switch was made, but older versions of K4PC will download the Mobi.. newer versions (I'm using 1.11.2 currently) will download the KF8/AZW3. (I think this is also the version you'll get if you download from amazon Website, in the manage Kindle Content section.) And, as already mentioned, downloading directly to device will net you the new file format that none else know how to read yet.

Edit: Not all books have a KF8/AZW3 format. If the publisher only supplied a book from older Kinglegen versions, they are only available in Mobi format. It's possible Amazon included this book in their automatic upgrade to KFX format, but only a Mobi version is available when downloading to PC.

The comment that you'll get the same book no matter how you download from amazon is dead wrong, The sad truth is, with Amazon, no one really knows what criteria will get you what version of a book, and everyone is working on trial and error. (Presumably, all these versions are generated from the same source, so the content should be more or less the same.)

Regarding the covers, that one is easy to explain though. Amazon treats the book and the cover as two seperate entities. When a book is send to the Kindle, a Cover is sent as well. Calibre actually does the same thing when uploading to Kindle from USB, but Calibre has to get it's cover from the book itself, (unless you download and add a cover image yourself.) Many books, especially those from the early days of E-books, do not have their covers included by the publisher. (I'm assuming, this is simply because they do not have an explicit license from the artist to include the cover image in e-book format, and since they consider cover in book file to be not that important, they just leave it out.)