Doctor Who will have 85 discs worth of material out by the end of the year (classic series and new series combined), and they're not quite halfway through the classic series material yet, and the new series is still in production. If you add Torchwood, that's another 6 discs of material.
Doctor Who could easily overtake Star Trek with a complete box set once everything is out on DVD. It'll never happen though.
Or how about a complete Disney Animation boxset, containing all the classics, all the shorts, all the Pixar stuff, all the DTV's.
Again, it'll never happen.