Ebooks, or Pictures of Books?
Project Gutenberg has over 50,000 eBooks in its collection. This is far fewer than Google Books, or The Internet Archive, or other large-scale digitization projects of historical items. An important distinction is that Project Gutenberg engages in the proofreading, formatting, markup/encoding, and other activities described above. Those other very large projects are primarily devoted to scanning, and then provide raw OCR output with a few automatically generated formats.
Such items are only partial eBooks — really, they are pictures (scans) of books, with some additional automated features. These are valuable, but do not provide the reading experience or quality of presentation that Project Gutenberg strives for. Using current technology, it takes human intellect and effort to convert a picture of a book to a true, functional, eBook.