The Steinway Piano, orchestral strings and voices come with the Jam Packs. This is not included in GarageBand. Did you upgrade from a Mac that had the Jam Packs installed?
You can now install all five JamPacks by buying MainStage 2, this will install the JamPack in a way that they can be used by GarageBand too. MainStage is much cheaper than the price for a single JamPack used to be.