As far as I understand, gas is paid out to the miners, but every node in the network runs each and every contract that is submitted to the blockchain. Doesn't this mean that other ethereum nodes are running lots of code for free? Also if every node is running all of the code all of the time, doesn't that mean that the combined computing power of ethereum is equal to that of just one computer?
If this is truly the case, then why is it being talked about as if it could replace things like AWS? If this is not the case, then how is the result of running a smart contract verified?
All of the resources I've been able to find on Ethereum are very hard to follow especially regarding this question.