Additionally the option to (relatively) easily transform markdown or richtext to another format is a great when you want to try a new tool and/or format.
That's the real secret, I think, keeping content up to date. Text isn't the only medium that can be treated that way, too. My family converted lots of analog audio and video tapes to DVD some years ago, and I immediately turned around and ripped them to digital, lossless types and stored them on a few hard drives and eventually a cloud backup. Will FLAC and MP4 last forever? Nope, probably not, but if I check in on these files every few years, update the players that I've saved (VLC), and periodically convert them to newer formats, I feel comfortable that my grandchildren will be able to hear their great-great-grandparents' road trip to California, or see video of my bar mitzvah on whatever screen they're using years from now.