Just wanted to comment on this. Libraries ARE able to purchase but BN and
Amazon, direct from publishers, from independant bookstore whereever. BUT they usually will buy books from a library wholesaler. The books from the wholesaler may cost a bit more but they come to the library ready to put on the shelf. If the library were to buy a copy from BN or Amazon, they have to wait for the book to arrive, then they have to cover the books, re-enforce the spine, enter it into their system, bar code it and then put it on the shelf. it's a lot of man power to do that but they can cut time and work out by purchasing from the wholesaler.
it also gets the books into the hands of the patrons faster. imagine you are dying for the new tom clancy. if you had to wait 10+ days from the release to be the first one to read it would you? maybe but if you could go buy it and you were a big enough fan you might. then the library loses that circ and if their circulation is down then what's to stop your town from cutting the library budget if it looks like people are using it less?
by using the wholesaler if the new tom clancy comes out on tuesday it will be on your library shelf tuesday or wed for you too borrow.
OP-i think its best to check with your library. as others have said every library is different.
Lara