rear firing tweeters....

I've always wondered about the "correctness" of rear firing tweeters as well, but I have heard several that sound good, so I guess that's what counts.
I had a pait of Nestorovic 5As for a couple of years, and they had an optional and removeable rear firing tweeter module on top. I always preferred it on.

Who is we ??

Some of the Revels use them; I am sure there are others. As I sit IN FRONT of my speakers I have never noticed a need for them! Just kidding.

I have a pair of VS2 Von Scheickerts which do have an "ambience tweeter/?high midrange " driver. It does see to add space to the sound but not much more so than a good tube output power amp qould ( I use both). It doesn't seem to hurt that's for sure. My main speakers, in a different rig, have better 3D halography (Focals) and don't have them. From that little experience I conclude they are not needed in all cases, the VS may be making up for a particular issue of their own.