I kinda like TCP vs. UDP analogy. Sometimes you care more about speed than precision. A few dropped items in a log. Not a big deal. I'd rather have that, than to be forced to use a more expensive machine for the job.
That said, I absolutely think the default should be the TCP way.
Look, I agree that in most cases you probably want to do everything you can to make your data 100% complete. But failed writes should be really rare, and there are plenty of times I'd trade the rare missing write for cheaper/faster database servers.