I like to think that Blocklanders are not real things and therefor do not react to things a real object would. They react to things that the game itself wants them to react to.
This is an interesting idea, but a big hollow sphere would be boring.
What would be cool is a huge system of labyrinth like caves that eventually leads to the center of the world. That would be really cool to explore, it wouldn't even really need bricks to be fun.