+1
People are having the same argument on music forums as we speak, only the argument is on CD's vs. digital downloads and streaming of music.
It all comes down to one simple thing: bitrate. An average person won't be able to tell the difference between CD quality of music and a 320kbps MP3. Audiophiles, however, will.
An average person won't be able to tell the difference between a proper blu-ray disc and a downloaded movie of the same resolutions. Some of us will. Especially those of us with 4k and 8k displays who need to upscale the video.
Here's the thing: A fully-fledged music album in 320kbps MP3 will take about 200MBs while a CD takes 700MBs. A downloaded 1080p movie will take between 700MB to 4.3GB depending on how much you're willing to wait for it to download (there are bigger files with even better quality but those are rare compared to the small ones). A proper blu-ray carries 25GB (single layer) or even 50GB (dual layer) of data.
All of the tremendous differences in file sizes are due to bitrate, which translates directly into quality (if you leave out bit depth, resolution and such). There's always gonna be a group of people who will go after superior quality.
Still, it all depends on whether or not the disc technology can keep up. Right now it goes up to 50GB per disc. Internet speeds around the world are rising rapidly. If they, at some point, find themselves unable to keep rising the amount of data that fits onto a disc by a huge factor, they will have lost to the internet entirely. That remains to be seen, though. Some say that nothing will come after the blu-ray. I'm sure curious if they are right.