The key with horns is to match them right. If you compare different types of speaker technologies with the exact same amp it might work - or not. Horn speakers as a rule expose any sort of system noise, and don't need as much power as a "standard" speaker, all other things being equal (a flawed analogy in this case, but hey :-D). Many say that horns and tubes are a match made in heaven, which I can't confirm or dispute.
The problems with topics such as this is that a single exception disproves the universal rule the topic tries to establish, since horn speakers aren't all the same, at all. To me what matters is how it measures, how it sounds, and how practical it is - no technology religion in audio over here.