Oh and by the way, you can't find anywhere near half of what's in print on some subjects on the internet.
And half of what's been in print is redundant. How many Thermodynamics or Calculus books do you need? How many have been in print?
(Largely the same economic scam as every new improved IPhone -- Professors gotta eat. Students shouldn't be reading textbooks by dead people and publishers need to have new products.)
No reason to suspect that an ONLINE textbook is incomplete or inferior. Otherwise, there would still be bookstores at Universities. Or haven't you discovered that there aren't any anymore (for the most part -- unless they have huge revenue on NCAA apparel and a joint deal with Barnes and Nobel..
As for citations to older journal articles. You can have somebody fetch it for you and deliver it cheap -- right over the internet.
I have a hard time getting my societies to continue to send me print versions of journals. You have a check the "I'm an old fart paper delivery" box.
How about you?