How much of High End Audio is Horn Speakers?

I have heard the AG Duos in four different rooms, including two small rooms and liked them in all instances.  The bass sounded more even and better integrated in the larger rooms, but there was plenty to like in even the smaller rooms—vivid, lively sound, and reasonably natural tonal qualities.  

Plenty of other horn systems, even quite large systems sound good in small rooms (look at Japanese audio magazines to see how many such systems are crammed into small spaces).  The waveguide of a horn reduces the impact of room interactions and so they can work well in smaller spaces.  I don’t know where someone would get the notion that 15’ ceilings are needed—explain what you personally heard (not youtube nonsense) that is the basis for this claim.
 

Well, if you never heard such a setup, you cannot comment based on experience.  As I write this I am sitting 8 ft from a horn setup in a most sized room.  I have heard few systems I like more than what I have (those too were horn systems), and I’ve heard quite a number of single driver full-range systems and multi-way systems with full-range drivers.  I might be persuaded to trade in my horn system for a two-way system utilizing a Jensen M10 fieldcoil full-range driver and a Western Electric 597 fieldcoil tweeter, but then again, maybe not.  At a much lower price point, I could live with a single-driver Charney Audio speaker (with the AER driver).  In other words, there is more than one approach to design that sounds good and there is no need to insist there is only one way, much less one particular set of components, that sounds good.

I think the Avantgarde speakers represent modern horn systems quite well--they are dynamic, engaging, and fun to listen to with no more tonal issues than any other speakers.  Yes, all speakers are voiced differently, so it may be the case that an Avantgarde speaker may not fit one's particular taste, but, none of the systems I heard were so extreme in tonal balance that they stood out in that respect.  Like all horn systems, they do require very good amplification, particularly at the low wattage levels that they will require.  I heard the Duos and Trios with both tube and solid state electronics; for me, low-wattage tube is the way to go.