I will admit that I can see that Roblox MAY have been inspired by Blockland. MAY HAVE. But comparing Minecraft to either of them and calling it a clone is just handicapped.
Minecraft is different in the sense that you do not build your world - it gets randomly generated for you and you build on it. The terrain, the caves, the ocean, that's all completely random. We all know that. Minecraft uses seeds - numbers that determine what your world will look like.
It's also different because it has the element of RPG in it - you gather resources to make shelter, cook food and thrive against certain monsters that come out at night. Unless you mod either game, Blockland and Roblox ARE A COMPLETELY DIFFERENT GAME!
Besides, Blockland and Roblox are better creative games over Minecraft, though I've seen some amazing things in Minecraft. But alas, comparing one of the most successful indie game in history to a hated game targeted at children and a relatively unpopular game made by one person who makes $20 with every sale is just pure bollocks.