Is every college textbook available on the internet ?

[AL1961]

My friend Carl says that every college textbook used in every college or university in the United States is on the internet . He also says the only reason college students buy their textbooks at the college bookstore is because they'd rather not wait for those same textbooks to download from the internet .

Carl seems to really believe what he told me, he wants me find some "college textbook" information for him on the internet . I don't think every college textbook known to man is posted on the internet .

Does this make any sense ? Why would a book be available on the internet, and in a bookstore at the same time ? Why should a book be posted on the internet, when it can be in a bookstore ? Would it really take that long for a book to download from the internet ? Is Carl right ? How can I find out one way or another ? Thank you in advance for your answers .