No one is suggesting that old books be thrown away. When you take into account the shear number of books being published each year (and the number is growing) it's physically impossible to have even a single copy of every book ever published available, even via a network of libraries.

Then take into account that not every book that get published has a digital copy, and every digital copy doesn't have a physical copy the situation gets even more complicated.

Not to mention VHS movie, DVD's, CD's, books on tape, books on CD, the list is endless.

When we stop looking at the library as a warehouse and more as a resource for more than just physical copies of things, the options increase exponentially.