Oh yeah that's true, shows like Xena, The Simpsons, and Ally Mcbeal had already had one-off musical episodes. I suppose that it's just become the expected thing to include Hush, The Body, and OMWF in any kind of lists of iconic Buffy episodes, just because they were such a departure from the Buffy norm and everyone always expects them to get a mention, but if we're talking about breaking new ground then Xena was the first that time

And agreed :)