You reminded me of something he wrote in the acknowledgements:

The membrane that has surrounded the writing process has been fairly permeable. Many concepts and ideas generated while working on the book have been allowed to seep out and have become part of a wider conversation; and, of course, numerous insights originating from the outside while the book was underway have been incorporated into the text. I have tried to be somewhat diligent with the citation apparatus, but the influences are too many to fully document.

Citations are one of the most important aspects of any non-fiction book, and even in this regard he acknowledges that he could not be exhaustive. To confirm the physical calculations implicit in a descriptive passage would almost certainly have been suboptimal. All to say, I am happy that Professor Bostrom is the one writing the Superintelligences of the world, and not the pedants.