Debngar - Scientifically they can look at how fast something changes/degrades over a certain period of time or under certain conditions and extrapolate into the future when that process makes something unusable. It is a prediction, but based on the best that we know at the time. I my experience is it's when the marketing types stick their noses into the process and 'nudge' the results and perspective to fit their ambitions. Humans are imperfect and so are some of our methods and the results, but we try. And if the disc only lasts 100 years and not 1,000 that would be enough for most people!
When Epson first came out with color inkjet printers they quickly found out that the colors began to change in less than 2 months! Ouch !!! Since then there have been great strides made in various types of color printing, and the 'estimated' longevity can be well over 100 years IF stored properly. Once again, I won't be around to see it fail.
I think optical media will have a place for a while to come. Thumb drives are still much more expensive than a disc, and when they fail - that's it, everything is gone - keep that in mind when getting a SSD (Solid State Drive). Most of us have high-speed Internet access but it's still not everywhere, so cloud storage services can be very helpful but not an answer for everyone yet. And not every TV can access the Web, so getting a show from the Internet to a TV can be problematic for many, especially if it requires more than picking a channel number! I also think people still like to have something tangible in their hands.
As for the DNSChanger problem, go here and click on the appropriate link to check:
https://forms.fbi.gov/check-to-see-if-y ... -rogue-DNS