Which I think is fine. Certainly more digestible to someone who has not been exposed to 37signals and doesn't want to read thousands of blog posts. There's a value-add to editing and distilling.
There's actually an academic philosopher whose blog I follow who tends to get exasperated that commenters misinterpreted some point he made 300 blog posts ago, or clearly must be unfamiliar with his work because he already discussed this question 250 posts ago. I always end up thinking, well if you would just write that stuff up into book....
I've also seen books that are literally the blog entries put onto dead trees, though, in original, unedited sequential order, which is definitely not the way to go.