Yes I ran into the same thing - It's disappointing, though maybe understandable as this is an iteration on the Primephonic app they acquired a while ago. And though I cannot find any reference to it anymore, if memory serves right, that was mobile only too?

I hope that over time Classical will make it onto the Mac as well. I listen to a lot of classical music while I work and it's more than a bit annoying that the play/volume controls on my Mac don't work...