Well, yeah.Just because people stop using them doesn't mean you discs don't work anymore. I still have about 50 HD-DVD's that we watch often. Same for Blu-Ray and regular DVD. The only drawback is HD-DVD players are hard to find nowadays but I have enough to get by.
But if people quit using them they won't buy new ones, and then manufacturers quit making them. Then when yours eventually breaks, you are out of luck.
Samsung has already stopped production of bluray players, as have some other manufacturers.