In Xilinx Virtex-4 FX FPGA series it means that there are real PowerPC 450MHz blocks (one or two) ready in the silicon of the FPGA. But if you buy (or design your own) PowerPC core IP, you can implement it inside any FPGA with the proper size of logic resources(probably not as fast as the built in capability of Virtex-4 FX). It will be "FPGA with PowerPC core" in both.