Why would anyone want Direct X, unless Blockland was to gain DX10 support, I don't see the big difference. Making Blockland into a DX10 game, for example; would mean that players with older computers would be unable or less able to play Blockland and get the best from their game. This would probably mean that players with older computers would have to upgrade their video system, and I know that there are some players who just can't afford to.
Other than DX10, and as far as I know; DX9 (and earlier) and OpenGL are basically capable of the same thing, the bigger difference being that OpenGL is Open Source.
Please correct me if I am wrong.