[WillPS]

The advantage of Blu-ray isn't higher resolution in these cases, it's the ability to have more content on a single disc. What would be a six disc box set on DVD could be two discs on Blu-Ray.

Resolution is only one part of the equation when it comes to picture quality. MPEG1/2 compression is 25-30 year old technology at this point and is lossy; liable to introduce visible artefacts which would not be present on an upscaled Blu-ray.