Linux/Unix just trust that if you want something persisted with certainty you'll do an fsync, if you do it will absolutely guarantee you're not losing that. It will absolutely make sure that your filesystem doesn't get corrupted by a power loss but if you didn't fsync your write you had no place believing it was persisted.

Doing that IMHO matches real world use much better. If I do a compile and get a power outage I don't care if some object files get lost. If I do an INSERT in a DB I do care a lot but the DB knows that and will fsync before telling me it succeeded. So making sync explicit gives you both great performance and flexibility.