Quite a bit of overlap here with unseen64.net, which, as you can probably guess from the domain name, has been operating since the N64 days, and still provides awesome coverage of cancelled, unreleased, or significantly-altered-upon-release games.
True, but the book seems to offer a lot of context about the companies and people involved.
I don't think there's a "but" here. Unseen64 also does that. We can have both. They made some in-depth videos a few years back on DidYouKnowGaming's YouTube channel.