[taming]

I may be wrong, but all of this assumes that the book in question is handed off to Sony or Kobo or any other ePUB vendor as a standards compliant book. If it is, then the DRM layer, whether kepub or Adobe, knows what to do with it and you should get a predictably consistent look from wherever you are purchasing it. There will be some variation based on what fonts are available and other things. I am clueless about Amazon.

Early on, Kobo's kepub format was not, IMO, very good. The stylesheet has improved, and now, with the Touch, you have the option of turning off Kobo styling, which, theoretically should get you closer to what the publisher intended. For example, kepubs seem, by default, not to have indented first lines in paragraphs. Now, with styling off, in some books the paragraphs are indented, in others they are not.