I suppose ZODB is such an expert application. It has to cope with systems that do not provide fsync(), but it provides degraded service on such platforms. It is very important for the database to call fsync() when it commits a transaction.
I'm not sure that ZODB *intends* to run on any system w/o fsync anymore. It had to before 2.3 because os.fsync() didn't exist on Windows, and ZODB has to run on Windows. I implemented os.fysnc() for Windows in 2.3 precisely so that ZODB would work better on Windows.
More mundanely, as I recall, we were having a specific problem wherein a backup script wasn't getting the correct size for a ZODB Data.fs file on Windows, and file.flush()'ing Data.fs didn't help enough -- backup kept screwing up until FileStorage's
if fsync is not None: fsync(file.fileno())
actually did something on Windows.