Yeah, and try to find a DVD player 100 years from now. Try and find a floppy drive (remember those from about 15 years ago?) and even if you could, try and find a computer to which you could attach one (well, maybe some of the last had USB ports). Remember VHS from not long ago? Even though one could argue people have enough invested in DVDs to make DVD players have some longevity, the same could have been said about all those movies on VHS tape. People seemed content to just go out and buy them all again on the new media format. And vinyl records. And cassette tapes. I guess you can still get players for all of those but they are definitely moving away from being off the shelf items and I bet many people don't have them.
USB drives are pretty cheap these days. Put the files on 8GB USB flash drives. At least that is a pretty current device format and it will be easy to transfer to whatever the next format ends up being. Will your friends have a computer with a DVD player in 20 years? I doubt it, they may not even have one now. A couple of USB drives will be cheaper than a pack of Taiyo Yudens unless you need to make 50 copies of this (in which case you'll probably burn out your DVD drive and have to factor that into the cost).