Wasn't MC recoded from the "ground up" about 2 years ago - specifically to free itself from all things Microsoft?
No. That's not how it happened at all.
MC had been coded in a largely cross-platform way for years and years before anyone ever saw any fruits of the labors. There were, and are still, exceptions to that.
* Theater View is a Direct3D application, and is therefore Windows-only at this time.
* Red October and the entire DirectShow-based video playback engine is, again, Windows only (because it relies on DirectX stuff).
The Mac version of MC has a shiny new video engine, but the Windows version doesn't use it, and Hendrik is writing that from the ground-up. Keep in mind that Apple only ships
one computer with a built-in optical drive option of any kind anymore (the "left over" 13-inch non-Retina Macbook Pro). So, I don't know that DVD support is such a big deal there, and they only just got video working at all in this version.
But, surely if they're going to build a new DVD Navigator replacement, it'll be done in a cross-platform way to work with Hendrik's shiny new video engine.