I think the issue with the AIP plates is that they are PDFs which means the text rendering is basically dumb (postscript-defined outlines filled with pixels). You need excellent res to see small text.
The Jepp data was designed for the poor 800x600 tablets of the era, and the data is vector based. Not just the graphics but also the text, which renders clearly at 800x600, whereas if you print a Jepp plate to a PDF and then view the PDF on an 800x600 display, it is a lot less clear (though still just usable).
The Kindle DX would be great if it supported directories.