From a completely non-tech person (me!): was there any technical reason why the UK DVDs had to be speed up but the BluRays don't need to be?
UK DVDs had to be in PAL, at 25 frames per second; the spec/players don't support any other option*. But TNG was shot at 23.976 frames per second; that meant that the show either needed to be converted or sped up; speeding it up is the standard that's evolved over the last few decades (and results in much higher picture quality).
Blu-ray added support for the normal film framerate, 23.976 frames per second, so film content can be shown "as is" without being sped up.
* Yes, NTSC is supported as well, but there's no guarantee that TVs could show it natively, and no requirement that players support converting on-the-fly, so there was never any chance that a major commercial house would support it.