I have met some wonderful miniaturists through various blogs, and this lady is no exception. She emailed me a tutorial on how to get this look in a miniature book without having to resort to figuring out how to get pieces of leather thin enough to be closer to scale. The brown ones are 1:12 scale and open with blank pages (I bound these pages myself using the longstitch binding method). I aged the pages using coffee/water and my embossing heater (when drying the pages, if you hold the paper in one spot for a few seconds the pages start to burn a little bit).
The blue one is 1:24 scale, but is not bound the same way. This ones looks like it could open, but it doesn't.
If you get a chance visit Nikki over at Witch and Wizard Miniatures - she is the one who showed me how to do the covers of these books.