> enabling subtitles was a profound difference for a subset of viewers (those who enjoy foreign media and the deaf) but even that came about with DVDs, not Blu-ray.
Closed captions were available on many, but not all, VHS tapes. Not all DVDs had subtitles either. The problem with CC on VHS was that it was often the first thing to degrade before the picture and then the sound.
Foreign films often had subtitled releases "baked in" to the video. Here's another hit of nostalgia. There were times you'd walk into a Blockbuster in the USA and the only available version of a hot new release was the Spanish or French subtitled version. You had to deal with the lost sections of image dedicated to subtitles in a language you might not even understand!
In terms of what they do for the user the difference is, in fact, incremental compared to when VHS first became available. VHS enabled you to choose what to watch whenever you wanted. Prior to that, you got whatever was on whatever channels you had access to.
I will definitely grant that enabling subtitles was a profound difference for a subset of viewers (those who enjoy foreign media and the deaf) but even that came about with DVDs, not Blu-ray.