I don't know what the degradation for NAND storage is, but another aspect that I didn't mention in my original comment is the fragility of disc based media. In terms of scratches and other damage.

You have to treat a blu ray very badly to get a scratch in it. It might look like a DVD or CD but it's not. It is much more resistant to scratches as it has a protective coating called Durabis from TDK. Sony uses their own proprietary coating.