Those book cases you get at places like Target and such are made from pressed wood. They fall apart really easily. I have a couple and I got rid of one because it looked so cheap and fragile when the wood started to bend down from the weight of the books. I still have two that I'm using for my DVDs but I'm going to replace them soon, I hope.
The ones I bought in Japan are actually much higher quality than the ones I bought back home, but they're still made of pressed wood. :/