Nice "source" you got there. A crazy blogger. And his argument is that... the US government did not defend the Forbes article on the richest heads of states. OooooK.
Anyway. It's very hard to calculate Castro's net worth. He does live in a palace, he does drive around in a fleet of black Mercedes, he does have servants and cooks and everything a rich man can desire. Forbes estimates his net worth in $900M, and explain their method
here. It really doesn't matter how much he has, fact is he lives like millionaire, or rather like a despot. So he has no incentives to get richer, because he can buy whatever he wants.
As for my other claim that the profitable parts of the Cuban economy are controlled by Party bureaucrats and Army officers, check this:
http://www.wsj.com/news/articles/SB116356024065223514
That 60% figure is just for the armed forces. If you include the non-military apparatchiks, it's certainly much higher.