Its just not a popular idea around these parts . There is also some factual basis for supporting this idea of using a matching vertical centre to your mains compared to a typical MTM horizontal and WM^TW design. Not only will matching a vertical centre provide the same power handling and sensitivity as the mains but will ensure matching tonal/voicing characteristics which is ever crucial to speech which as humans are very critical of and other soundstage shifts. Not to mention off-axis response which has been shown in some cases where the vertical matching centre is superior to the horizontal centre off-axis of that same brand. This is important if you are not sitting in the "sweet spot".
The biggest benefit of a horizontal centre is ease of placement and WAF (wife acceptance factor). This is a big plus and why most of us tend to use them.
