Decentralization and auditing. If you put some code on AWS there are two potential issues.
Firstly you don't know if AWS has actually run your code. They could potentially replace your code with their own modified version which does something malicious (like add a bias). For example in a voting system, code could be modified to ignore X percentage of unfavourable votes, or change unfavourable votes to a more favourable candidate.
Secondly I don't know what your code on AWS does. This isn't great for financial and voting systems that should be audit able.
With Ethereum you can view the code for a contract to validate it does not "cheat". You can also trust the contract was executed correctly because the miners have validated it and added it to the block chain.
Firstly you don't know if AWS has actually run your code. They could potentially replace your code with their own modified version which does something malicious (like add a bias). For example in a voting system, code could be modified to ignore X percentage of unfavourable votes, or change unfavourable votes to a more favourable candidate.
Secondly I don't know what your code on AWS does. This isn't great for financial and voting systems that should be audit able.
With Ethereum you can view the code for a contract to validate it does not "cheat". You can also trust the contract was executed correctly because the miners have validated it and added it to the block chain.