Sure, the article itself can explain it: "But analysts say the embrace of Power has two crucial advantages for Google. First, the Internet giant builds its own data centers and tweaks the technology in its server computers, and the licensing regime in the Power foundation is hacker-friendly in a way Intel’s handling of its intellectual property is not. The second advantage for Google is negotiating power..."
I read the article and didn't find their little explanation to be that good, that's why I asked. Why PowerPC? Why not SPARC or ARM? What got them this involved?