My only conclusion would be that the masses have developed the mentality that a horizontal center channel configuration is the 'correct' way to do it.
There's some truth to that. I'm sure a lot of it IS simply because horizontal centers are what everyone sees, but the reason horizontal centers were made in the first place was so they would fit below the screen. Most people simply don't have a way to accommodate a vertical center, but you have to wonder how many more people would make the space for a vertical center if they knew it would improve the sound.
