An 80 Plus rated PSU is effectively necessary these days. Especially when using a unit this size.Well 71% isn't horrible. They definitely need an 80%+ unit in the new Mac Pro though. It would make them look better.
To me, the 71% says Apple was cutting corners to improve their margins. 🙁
BTW, if you run the math at the max sustained rating on wall voltage (125VAC), the efficiency drops even further to 65%. 😱 🙁