You're taking up 63 megabyes per book?
Yep. These are scans. Born digital content and manually proof read stuff like Project Gutenberg is of course much smaller, but for images of each page for 100 to 1000 pages 63 MB is about average.
it is like an article featuring a new sports car that does not mention its horsepower.
To put in a way that slashdotters may understand, it is like an article featuring a new processor that does not mention it's clock speed.