This is true, but it is generally true. Even for UV-EPROMs the retention time can be as low as a 25 years, if kept warm, even with the window sealed correctly. Magnetic drives are quite a lot better, around 50 years.

CD-RWs are somewhat wider in their stability, I have ~20 year old discs that are becoming unreadable because the actual foil is delaminating from the plastic disc. Meanwhile I have ~40 year old DS-DD floppies that are still fully readable even though their medium is in physical contact with the read/write heads (although here, again, storage conditions and especially the different brands/batches seem to make a difference).