I don't see any (future) updates confirming Direct3D as a render option, I'd have to base a reason off this image from runescape.wikia.com.
Look at the way the water is rendered on the OpenGL side, kinda pureish, but if you think of water in a more realistic kinda way, then I see why Direct3D renders the water that way. Blockland isn't like Minecraft where you can Mod Shaders/Shadows (Forge Shader Mod), maybe OpenGL is easier to program with.