There's a big amount of savings though, beyond the obvious production cost savings (and yes, its alot cheaper to produce a digital book than a physical one),
First of all, fewer books also means fewer trucks
Secondly, there's a big savings on storage space. Publishers no longer have to store books at warehouses, if the book is in low or unknown demand.Small publishers who can now operate without large overheads and large publishers can now cost effectively sell their backlisted items (took this bit from wikipedia).