This is primarily an issue for contract writers[1], of which there are relatively few. You get similar kinds of automatic exploitation on exchanges of all kind

This is primarily an issue for contract writers[1], of which there are relatively few. You get similar kinds of automatic exploitation on exchanges of all kinds too (stock, currency, futures, etc), though I think it's fair to say Ethereum makes it (quite a bit) more complex and more automate-able on average. [1]: transitively it affects users too, but it's a bit different either way.