Any long term archive strategy has two big challenges, hardware and software obsolescence. Any data that needs to be saved over the long haul needs to be moved on a regular basis to a new storage technology. While these discs may be stable enough to be readable for many years into the future, the more important question is will the hardware to read them exist 20 years from now. How many people have stored data on tape cartridges, zip drives or Bernoulli boxes only to find that when they needed to use it the hardware that wrote them failed and could not be repaired or replaced?
The same goes for software. I recently dumped archives of all kind of stuff I did in grad school because it used graphic and other software that is no longer available for the current operating systems and the file formats are not importable into current software packages. One advantage of throwing your old photos into a shoebox is that so long as they don't get physically damages you can always pull them off the shelf and look at them.
With electronic storage it's not always that simple.