PowerPC as we know it, i.e. a cpu for general purpose computing, is gone. It's now an open standard (The Power Architecture) and its descendents include the Cell processors used in the PS3 and XBox 360.
They abandoned the PPC platform because the chip makers, IBM and Moto were unable to keep up with intel on the performance front. Additionally both chip manufacturers continually had issues providing apple with chips in quantity.
It makes zero sense to abandon a platform that has revitalized and transformed the Mac.