Does PG really need a book? Maybe to make a little money, or for the vanity of being a published author, but his legacy is online. It's just the new medium.
I prefer to read physical books, for anything I care about. At this point the web is more of a replacement for low-engagement mediums like newspapers than books.
Personally, I prefer reading words on a printed page over a computer display. Print offers much better resolution, a more natural way to read (for me), and I'm not distracted by email/blogs/work.