Disney has released DVD editions of almost the entire Studio Ghibli library over the last 10 years. Two weeks ago, they released the first Ghibli Blu-ray (last year's Ponyo) and reissued three titles with some new extras (Castle in the Sky, Kiki's Delivery Service, and My Neighbor Totoro). One would assume that catalog titles should start hitting Blu-ray later in the year, and that the DVDs were a means to an end: getting three of the other early Ghibli titles refreshed alongside a jumping-on point (Ponyo) in advance of Blu-ray mastering.
All previous DVD extras on Castle, Kiki, and Totoro are intact, with new mini-featurettes focusing on the development of each film. If you have the previous editions and want the Blu-rays, there is no logical reason to double-dip on these. Netflix them for the extras if you're a Ghibli enthusiast.
Parents with kids re-buy titles multiple times (even the same edition) due to misplacement or damage, so I'm not as virulently opposed to these re-dips being put there instead of/without Blu-rays. Since John Lasseter took the reins at Disney Animation, he's settled for nothing but the best, and for animated films from the early 80's, I'm sure he wants them to look as theater-perfect as possible.
That said, the Ponyo Blu-ray is a delicious taste of what's to come. Since it was done in the same hand-made style as the rest of the Ghibli catalog, one can easily assume we can expect similar clarity and color depth from upgraded versions of the Ghibli library classics. The Ponyo disc also includes World of Ghibli featurettes in the same style and application as the other titles.
The prominent treatment within the Disney family that Lasseter has pushed for Ghibli is really the essential third leg to a revived animation legacy. The Disney hand-drawn classics were my childhood, Pixar carried me into adolescence and through my teenage years, and I discovered Ghibli just as I was getting ready to hit college. The Disney animation family now touches just about every niche, with upcoming stop-motion features solidifying their fourth leg. It's a great time to love animated features, now that the flagship animation studio is leading the way. With their example, others are challenged to create even more innovative, amazing worlds.
*The literal translation of the Japanese title is Laputa, Castle in the Sky. Unfortunately, anyone moderately spanish-speaking would read that as "La Puta" (the whore) instead of Lap-uta, as it's actually said, so they chopped off part of the title for US release two decades ago. The reason for the chopping could be as simple as keeping the title bland and generic (US audience-friendly). Similarly, Ponyo's full title is something like Ponyo on a Cliff By the Sea.