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%.