Actually, no, if everything is minimalistic, everything is. It's not a relative term, it's more of a specific quality and philosophy.
Same way if every new paiting for some reason starts being pointilistic, they don't cease to be pointilistic just because its the absolute norm.
(And even if it was a relative term, we do have experiece with non minimalistic software from the past, so we can still considered a current crop of software were everything is much more sparse and streamlined as "minimalistic" compared to that).
In any case, we're not talking about everything, just these two and any other that fits the description.
Which ebook reader does something horrible here? When not adjusting settings or loading books, most of them just display a book-like page. I haven't encountered one yet with Office-like toolbars or whatever Acrobat thinks it's doing.
"No skeuomorphic book shelf" seems like a low bar.