If you've seen the interview session video where link is one the farm you'll notice he uses the leaves of different plants to summon epona and a hawk, does this mean there is no instrument and can only summon said critters at a certain place? Or is this just for tutorial reasons? Also people whine about link being a "cowboy", well there is no japenese word for "shepard" or "farm hand" so they just call it cowboy so they can understand.
They did the same with OoT, though they put it as an item.
As for shepherd, they do have a word for it. It's hitsujikai. However, I believe it's rather rare in Japan, and that's why so few Japanese people understands it.
Yeah but with the fairy ocarina you could have it anywhere, but if you watch he just goes up to a plant with weird leaves and uses them like whistles.
They probably will have an instrument in there somewhere. It seems to almost be a tradition now. As for the special kind of grasses, I'm not too sure what the deal with that is going to be. They might have it so that only those grasses can call the hawk and horse or the grasses could just be until you learn a song on an instrument (most likely an ocarina, but it could be a tenor sax. :P ).
Your explanation is what I was thinking also since it's at the very beggining of the game.