The PPE core is a completely new design (it isn't even similar to the G5, let alone derived from it). The WSJ article is correct; the PPE was originally part of Cell and it was later improved (with additional instructions) and used in the Xbox 360 processor. Even though they both share the PPE, the two chips have radically different architectures because of the SPEs (or lack thereof).

I found it interesting to watch these design processes from inside IBM; I'll have to check out the book.