For whatever reason, Mill Creek bought/acquired Sony's previous catalog, which is why you see so many re-releases of previously released sets, both single season ("Bewitched", "Partridge Family" etc.) and "complete series boxes" (again, "Bewitched," "Partridge", as well as your referenced "Mad About You", "Party of Five", etc.); however the newer, cheaper MC versions invariably utilize "cheaper"(looking) bare bones packaging and utilize fewer discs as they cram more episodes per than Sony originally did. What little I know & understand about the tech downside of this, to be honest I've never done an "A/B" comparison but the gist as I understand it is that putting more episodes per disc means the video information is more compressed which results in lesser picture quality. Makes sense to me.
Given that I'm a "collector" and would eventually likely bought both versions anyway (at least those titles that were duped, not all were), I'm still glad and prefer to watch the original, less eps on a disc releases put out by Sony (where it applies, by title).
CBS Paramount however at least in the case of those titles with which I'm familiar, seems to have simply taken the same discs per season from their single season sets and collected them in new (albeit rather simple) packaging, as witnessed in the complete series box sets of "I Love Lucy/TLBDAS", "THe Lucy Show", "Medium" and from 20th Century Fox, "Reba" and "The Mary Tyler Moore Show". Thus, I would stick with the original studios' version of releases (instead of Mills Creek), single-season or complete series box, whenever possible.
But then I'm a geek what do I know?