I was not trying to attack you or anything, so if I came across in that way I'm really sorry, it was not my intention (and if I looked like I was being defensive I'm a PLD, I can't help it!

). Seriously though, the point I was trying to make though was that change was made long before FFXIV, and I admit my previous post missed some more information that would make it more clearer, so I'm sorry for that too.
Prior to FFX the FF games used a turn based or the Active Time Battle System (ATB) and a generally 2D top-down view sprite generated or '2.5D' prerendered environment, so having a text box above or near the characters was to make it clearer to see who was talking without obscuring other important characters or details.
With the move over to real-time 3D graphics and polygonal character models and environments however, with the ability to move the camera around, simply having a text box at the top would likely obscure other characters or details, so keeping the text at the bottom with no background window box makes it less likely to intefere with what is happening on screen, by making it more subdued (this also coincided with the use of actual voiced dialogue in cutscenes as well). And FFXIV is no different, it's a design choice for using 3D real time graphics and environments.