The piano is only a medium really.
Just a medium? How sad!
Though I agree. I think the countless transcriptions from piano to orchestra of pieces by various composers through the ages prove that anything that can be played on a piano an orchestra can make "bigger and better" both in texture and in creating extra lines, 'read,' counterpoint. Though that isn't to say there aren't a lot of orchestral adaptations of originally piano music that just seem pointless...
I had a listen to Albeniz's Iberia for Orchestra and I honestly think it was a lesser version of the original. I'll admit, the percussion section always throws in some nice gimmicks, and theres something to be said for the awesome sonority of the trombone, but even so. There is something nice in instrumental music about only having one texture, and IMO therein lies the true beauty of solo piano music