Just posting to say that, of course, I have had the same experience.
And I guess we all agree that it is safe to say that every owner of a raspberry pi that gets into scratch and says "ah ha, let's check out this impressive 128-instrument feature that will allow us to play trumpets and tubular bells" ... will have the same experience.
I'm a giant fan of the raspberry pi, and furthermore, I would say that, hey, part of being exposed to the "guts" of a computer in the way that the raspberry pi makes possible... also involves that occasional experience of "oh, i guess there is no driver for that... I would have to learn how to make that work."
BUT, in the end... it would be better if someone made either (1) a clear installable patch of some kind that maybe activated a possibly crude version of just 16 of those voices... if not all... or (2) at the minimum made a clear official announcement about the state of the voices in Scratch and why they don't work and what would be needed for them to work. That way instructors and parents could say to kids... "that one feature is not working because there is no XX on this computer now... if we are lucky, in less than a year, some smart community member might make that happen."
So... just a clear post from a Pi Person telling us what is up... would take care of the basic need.
If you are an actual Pi expert or member of a development team, please make a note of what we're saying here... or forward it to someone!