They ask you to send ETH using myetherwallet is because they have to send the tokens back to the address from which they recieved the ethers, that's why they say that don't send ether from an exchange and also in case of a conflict or confusion you would not be able to provide enough evidence to support your claim, also don't forget that myetherwallet wallet is one of the best wallet provider for ethereum. And it is always nice to be in control of your funds as the exchanges can be hacked due to a security breach.