Almost... commercial CDs and DVDs are "cut". That is, they have a solid substance that is etched out and given pits to represent the digital data.
CDRs and DVDRs are not cut, they are burned. They have a special dye that reacts to lasers during the burning process. Dyes are much more susceptible to degradation and other processes.
Also: take a cheap, blank CDR disc and scratch along the top of it with a key (the label side). Now turn it over. You will be able to see through the CD. Why? Because unlike commercial CDs that protect the medium on top and on the bottom, the dye used in CDRs is just put directly on top of the CDRs.
You shouldn't fear scratching the bottom of the CDR (what we usually worry about with CDs) as much as scratching the top. Also, whatever binders they use to keep the dye on top of the CDs can get loose over time, causing the dye to flake off.
Higher priced CDs and DVDs tend to be made of better stuff and to last longer.