There's might also be a difference about principles. If I'm remembering past disagreements properly, and I might not be, Robert believes that we should try and find principles for playing Go well, John believes that any such principles are likely to be very high level (focus on "time", "make your stones efficient"), relying on developed judgment.
So perhaps John just thinks this book is just fine without general principles, while Robert will try and bully someone for calling something excellent when it doesn't contain general principles.
John will probably correct me about the subtleties of his own views, but I wanted to make a general point. We can disagree about the role of principles in learning Go, and we'll probably have periodic debates about it on the boards. But coming in to someone's book review and saying "you can only call this book excellent if it has principles, of the kind that I want" is unseemly.
If you want a genuine discussion of the issue, start one, ideally in a new thread. Don't just tell people they've reviewed books wrong based on your idiosyncratic standards.
Debate is good, but this seems more like policing people's comments.
References: I'm thinking of comments from John like this one:
viewtopic.php?f=17&t=2458&p=40926&hilit=principles#p40926. Here, John talks about principles, but high-level ones:
viewtopic.php?f=12&t=1578&p=29876&hilit=principles#p29876.
