The name is just a distinction without a difference. Kai is the DBZ series heavily abridged, that is plain, so the presence of the Z is certainly not without merit. In fact, to me, it always should have been there simply out of principle--in my judgment Kai is DBZ in the sense that it's basically the literal story that Toriyama wrote. All that padding in classic DBZ we'd mostly call superfluous if it were happening in the present day. And we do--many fans dislike parts of Naruto Shippuden and Bleach.
In sum:
DBZ = Classic series adaptation
DBZ Kai = Originalist DBZ
Fair enough, no?
Karl raises a good point about TV. I wonder if Cartoon Network cares anymore? If not, well, Shippuden could always use a companion on Disney XD...
On the release timing, I make no assumptions whatsoever that it's at all problematic. Dragon Ball sells, there are fans that likely prefer (or can afford) one or the other, and there are people that will actually buy both. Not to mention that if Kai eventually adapts beyond Namek, Funi will be well into its work on the series already.
16:9 is the broadcast version, correct? In any case, this I still do not understand. Why put out different aspect ratios for different format releases? Why didn't they just broadcast in 4:3 if they considered it the best video for the Blu-Ray? Were I Funi, I wouldn't be sure what to pick. I suppose 4:3, since a Blu-Ray release of this is probably a sure bet? Assuming they actually choose and don't just emulate what the Japanese did, that is.