The only difference is whether technically copying happens, because controlled digital lending has the same results as a system that involves no copying. It doesn't have the common definition of copying where two people can access two copies at the same time.
If IA came first, and libraries came second, would we refer to libraries as having a technicality/exception that lets them be legal?
Though I suspect that if libraries were invented right now they'd be declared illegal.
Please look at what I'm actually saying instead of snapping off replies that don't address my point. (And yes I edited in another couple sentences but the part about libraries not copying was in the original version of both those posts.)
(You're fine editing; I edited too, just for clarity).