I guess my perspective is this - I don't verbalize information that could potentially be perceived as coaching/aiding one team or the other. If I say no catch, I'm essentially telling the runner to run. Depending on the batter, that could mean an additional 1 or 2 seconds between me saying it and they noticing it and possibly the difference between safe and out at 1B.

If I say batter's out, I am making a statement of fact to prevent the batter from causing a state of confusion he does not have the right to do.

We don't tell coaches when to bunt or what pitch to throw, so why should we tell batters when there is a D3K?