According To expect they always say blockchain can never be hacked and your information can never be stolen .. But day in day out Hacker are hacking crypto exchanges to steal people asset , ETH Suspended hard Fork because of security reason . HitBTC and Cryptopia are understand maintenance because of hacker . Are they Using block-chain technology to deceive Us ?...
Not sure why you mix centralized exchanges into block chain. But any block chain can have a bug. It all goes to how many eyes there is to check the code and how many people test on testnet before it goes live. You can notice difference between Monero and Bitcoin towards Etehreum. First two are making baby steps not risking bugs. Ethereum just jump no matter what will happen. They can rewind their immutable code anyway.