I've also wondered in the past how the short-throw horns in some line array designs could get the HF to the back of a concert venue. However, for the most part, I have nothing against line arrays, as they have their place in pro audio. I was mostly curious about why the horizontal, arced point-source systems had mostly disappeared. Based upon the recommended reading and responses, I've arrived at two conclusions about horizontal VS line arrays:1)You can't get away from imperfections in any arrayable system (such as lobing error and comb-filtering, etc.), but most are less obvious in vertical line arrays. So, you have to be more careful about the design compromises you choose to tolerate for the horizontal.
2)Since horizontal tight-pack systems aren't truly "point-source" because they can't actually emit from a common locus, your choice of components and their arrangement becomes more critical than with vertical arrangements.
It seems to me that redesigning the horizontal tight-pack array of olde is more of a challenge than it is an impossibility!