It's actually worse than that. You're basically encoding a digital stream of data using an analog method in uncontrolled conditions and then reading it back off. The laser, the disc, and the motor are all not perfect and it is extremely difficult to get a perfect burn. On top of that, you have to deal with aging and disintegration of the dye layer in burnable CDs/DVDs.

If you're archiving data on CDs/DVDs, it would be worth your time to read a bit on cdfreaks.com, which is a good community site dedicated to CD/DVD burning. Essentially, you need to buy a good burner (most are not) and good media (again, most of what you find in stores is bad), followed by storing the burned DVDs in a cool, dark location. It's a bit more expensive, but the results are apparently worth it.

As for data stability, I'd say the order goes something like:

1. Flash (especially the more expensive models)
2. HDD (more vulnerable to physical damage and moving components)
3. Tape (more stable than CD/DVD but tape head problems)
4. CD/DVD

Unfortunately, tape is too expensive and cumbersome for most people.

As for myself, my long term backup strategy includes everything on an external hard drive + 3 backup DVDs (per block of photos) stored in different locations. If I had more time and energy, I would also probably use an additional external drive and rotate the two between safe deposit box and home as well as using a RAID configuration for the external hard drive.