I think you are looking at it wrong; its like saying a bank teller or stockbroker or even a cash machine has no 'useful industrial application'. They are necessary for the currency to work, and they must be paid to do a job. I suspect paying a cryptocurrency miner their 'fee' is a lot cheaper (per transaction).

There's a non-zero cost with making stock trades, keeping money secure, and transporting money into an ATM machine.

There is a practical (as close as we can get) non-zero cost for moving bits around the internet. It seems like there should be a similar mechanism for building trust in the blockchain.

>Not so sure about Cryptocurrency

In the case of PoW cryptocurrencies, like Bitcoin, the token is the reward for the useful application: verifying a series of transactions.