There is a role for summaries with different levels of detail. The short capsule summaries are useful(for one thing, it is easier to remember) and your link itself is a great example.
But, there is also a role for longer summaries, which are still short relative to the book, but include useful points and some of the illustrative examples not present in the shorter summaries. Reading a 250 page book has ample scope for the mind to wander and lose track of the important issues which is not an issue with a 10 page summary.
Further, summaries at this level are less available, and it would be a good thing if more books had such summaries. (The downside being people might be more likely to skip the original book and the author is not rewarded - this can be corrected to an extent if the author themselves give these shorter summaries at the end of the book or as a separate short book. Also, some others might be motivated to get the original book after reading the summary).
But, there is also a role for longer summaries, which are still short relative to the book, but include useful points and some of the illustrative examples not present in the shorter summaries. Reading a 250 page book has ample scope for the mind to wander and lose track of the important issues which is not an issue with a 10 page summary.
Further, summaries at this level are less available, and it would be a good thing if more books had such summaries. (The downside being people might be more likely to skip the original book and the author is not rewarded - this can be corrected to an extent if the author themselves give these shorter summaries at the end of the book or as a separate short book. Also, some others might be motivated to get the original book after reading the summary).