Ok so we know that there are issues with Microsofts XBL closed environment and XIV being released on it, this thread isn't so much about that but DirectX.
I've read before about DirectX 10+ (10, 10.1, 11) not being compatible with the 360, I think it was on 1up so take it for what you will.
Anyway what I'm getting at is the possible reason the XIV doesn't currently support 10 or 11 is because they coded the PC version not as the PC version but as a 360 version.
I know, conspiracy theory.
But what I'm thinking is that eventually SE will move on past that and move to a PC only development (assuming they can't work thinks out with Microsoft, if they don't it's a bad thing for all of us since saturation is key) and eventually add at least DX10 features. These would lessen the load on GPUs as they could get similar effects with less stress, and then if they could get DX11 in there... I forgot where I was going with this, but I'm pretty sure that each upgrade of DX has an increase in physics and graphic quality for less system costs... ok depends on your card and tesselation definately hurts alot of cards...